Minecraft Wiki:Issues

This page's purpose is to list all the bugs players have come across. They pertain to the unmodified, unhacked game. Most of the single-player bugs also apply to multi-player.

Version history also contains bugs that aren't listed on this page.

Bugs and feature requests can now be logged at Get Satisfaction: Mojang.

Notch will focus the Beta 1.6 update on bug fixes. He will be going through several bug lists, including this one, and fixing the bugs mentioned.

General

 * If Java runs out of memory, Minecraft will crash to a black screen without saving any chunks. The inventory, player position, momentum, and time will all be maintained, however, as these are stored in the level.dat and are constantly updated. GetSatisfaction thread
 * If the player stands at X:1000 or X:1001, The block at X:999 or X:998 cannot be targeted from the side. => This happens much more often than just every 1000 coords. Probably its between some chunks. Also when you cant target the block, you will target block behind it instead.
 * Advanced OpenGL will often clip visible areas, especially if you rapidly turn your mouse.
 * After Minecraft crashes and a save is recovered, your achievements and statistics are reset.
 * Sneaking prevents movement from Soul Sand or Cacti to any other block.
 * If you are sneaking when you exit the game, when you reload the game you fall into the block below you, and onto the block below it instead which can cause Suffocation if there is a block of air directly below and a solid block underneath.
 * If you hold the left mouse button down while holding a item, then open your inventory, still holding the left mouse button, and then close your inventory, as long as you don't release the left mouse button, you are able to break blocks without the swinging item animation.
 * A bug exists where the game may refuse to remember custom controls after updating (not to a specific version - just updating in general). This is caused by one of the values in Minecraft's "options.txt" file being unset, usually the "lastServer" field - attempting to connect to any multi-player server address (valid or otherwise) typically resolves the problem.
 * On Linux, Minecraft is losing its mouse focus on every click to X Window for a very short time. If a pressed key is released at this moment Minecraft won't register this. This will cause you to move even if the movement key isn't pressed anymore. This is due to a bug in LWJGL that was fixed in LWJGL 2.6. Replace Minecraft's copy with a newer version of LWJGL to fix this issue. GetSatisfaction thread
 * Sometimes mobs within a certain area will stop moving, and entering the area will cause the player to become rooted to the spot and often vibrate wildly. Many animations, such as digging and health recovery will be broken, and mobs that the player hits will constantly loop the damage animation without dying.  It is not possible to catch fire.
 * If the player adjusts their system clock one hour forward, the game will run abnormally fast, allowing quick movement and mining. Changing the time back, exiting the game, setting the time forward again, and re-entering the game will allow you to change the system clock properly. Note that the inverse of this is not true--setting the time backwards will not slow down the game. This is caused by the method used to separate game speed from FPS, which involves comparing the system time between the last game loop and the current one.
 * The audio position of the player lags behind where the player actually is. The supplied OpenAL DLLs lack 3D audio so it's hard to notice. However if you replace these DLLs with alternatives (such as the ones provided by the Creative drivers) you can notice that when you walk the footstep sounds are generated from where you were coming from, rather than directly underneath you. It is disputed whether this is a bug because it is not noticed with the provided DLLs, and 3D audio is something the game was not intended to support.
 * Selection bounding box breaks ATI card's Anti-aliasing. (Certain ATI cards don't support anti-aliased lines.)
 * The hat layer in a player's skin is in an incorrect position when sneaking.
 * Direction is not restored when resuming a saved game. This is problematic when attempting to create frame perfect segmented recordings, such as segmented speed runs of Adventure Maps.
 * After restarting a computer minecraft has extremely high contrast even though all other programs are fine.
 * Billboards (Items and torches) align to the players view plane, not position. (When you look at an item to the far left or right of the screen, it will be distorted
 * Theres a file called Map.txt in the minecraft files that causes performance issues. removing it may great increase your performance, but may reset your achievements

Armor

 * When swinging your arm, the arm on your chest armor doesn't swing with it.

Audio

 * If the graphics are set to "Fast", the sound associated with rainfall will not play at all. Though you can still see the rain on either graphics settings, you can't hear it on Fast. (Confirmed)
 * The openAL32.dll and openAL64.dll that come with Minecraft do not work properly. This sometimes causes Minecraft to crash when players turn sound on in the options menu. On Windows machines, deleting Minecraft's openAL files usually solves the problem, because Minecraft will then automatically use Windows operating system's copy of the openAL dll, which works properly.

Arrows

 * Arrows that hit doors can float if the door changes its state.
 * They also appear to collide with fences, portals, and sugar cane. Arrowsugarcane.pngArrowportal.png
 * Arrows that have not hit a mob become unobtainable if you die or save and quit then begin playing before retrieving them.
 * Tilling dirt with an arrow on it will cause the arrow to fall through into the next block.
 * Arrows that a player shoots rapidly occasionally hit said player. More common in SMP, most likely due to lag.

Beds

 * When sleeping and holding left mouse button a block below the bed gets destroyed
 * While sleeping, particles (torches, furnaces, etc.) do not "adjust" to face you, some of them may look flat or even be invisible.
 * Beds placed in fully enclosed areas (on both sides and with only one space above), or beds placed with no ground even with the block under the bed on either side (with only one space above), can cause you to wake up inside a wall, killing you and potentially destroying your items. This is due to player placement when you wake: if the game cannot place you on the ground level with the block below the bed on either the left or right side, it will place you on top of the bed. If there's only 1 block height above the bed, your head will become stuck in the ceiling, killing you.
 * Beds cannot be placed on snow.
 * Putting a Powered Rail in the front of your bed will make it so when you wake up it will still be night, as if you never went to sleep. (Only tested with the powered rail on)
 * If the player right-clicks the bed fast enough, they will recieve a message saying: "This bed is occupied" even though they are on SSP. this is caused by the last click to attempt to get in bed being performed during the game placing the player in bed, tricking the game into thinking someone is already there.
 * Temporary fixes for mobs inexplicably attacking during sleep include: having at least 5 spaces between the bed an the nearest wall, breaking and replacing the bed, having door on the same level as the surrounding (outside) ground and replacing the floor with glass.
 * Beds being broken appear to get brighter.
 * If you place a bed on the highest level of the map, it will be lost.
 * You can sleep while in a minecart. You still move with the minecart but sleep through the night.
 * You can sleep during a thunderstorm, even during the day.
 * If you walk very far away from your bed and then die, you do not re-spawn at your bed and instead spawn at your original spawn point, receiving the message "Your home bed was missing or obstructed".
 * If you have a bed surrounded by slabs, entering the bed will result in the "sleepwalking" glitch.
 * If you create a 'bunk bed' (this is done by placing two blocks down, placing a bed on top, removing the two blocks underneath and placing another bed), sleeping in the bed beneath will always trigger a mid-sleep zombie attack, even if you are in an enclosed space which is well lit.

Boats

 * Boats will collide with a snow layer as if it is a full block when placed on land.
 * If you manage to stand on your boat while it is under water, the boat will be unable to rise. The boat will still retain horizontal movement, though, and will often slide out from underneath you.
 * If you go under a water stream your boat will accelerate and rise upwards. This is an error in the programming of how boats float. (This bug is often exploited for making water elevators, the fastest non-mod means of vertical travel)
 * If you save and reload while in a boat, you will no longer be in the boat.
 * Pressing F5 whilst in a boat will show your leg/foot armor protruding from the bottom of the boat, even though your character is sitting. The leg armor will also fail to properly adjust to still be around the player's legs and will still be going straight down as if the player was standing still.
 * You can also see two pairs of legs while in a boat if you enter your inventory.
 * If you place a boat on the ground and drop sand onto it, the sand will repeat the falling animation on the top of the boat and you will be able to pass through it. Reloading the world will properly place the sand, but the boat may be dark as if it's in an area with no light.
 * Exiting a boat will sometimes cause the player to fall through it. This could be fixed by implementing code that would place the player one block higher than the boat when it's exited.
 * Exiting a boat on a half-block like a stone slab makes it nearly impossible to move. Half-blocks make nice boat docks or grounding areas except for this bug.
 * If an occupied boat crashes into an unoccupied one, only the occupied one breaks.
 * If you enter a portal while in a boat, Minecraft will crash.
 * Boats, like many objects, are invisible at the top layer of the map.
 * If you want to attack a mob in the water, your boat breaks when you attack with the sword.
 * It is also possible to destroy your own boat with arrows, even when not looking down towards the boat, making it virtually impossible to attack from a boat.
 * With boats it is possible to fall from high places with out taking damage if you are inside the boat when you hit the ground.

Buttons

 * The hitbox for the button is displaced halfway into the block of air it occupies. Targeting the button itself will only hit the block behind it.

Cactus

 * Cactus also has a South/West rule for applying damage. Placing a block above a single cactus piece prevents you from stepping on the cactus and prevents you from taking damage by pushing against the south or west sides of the cactus. The north and east sides of the cactus can still hurt you.
 * If a door is placed beside the cactus it will break the cactus and the bottom part of the door, leaving a breakable collectible "window". It is collected by placing another door in front or behind or even the the side of the door to collect the "window" as a normal door. This bug only occurs with wooden doors.

Chest

 * A chest can still be opened when a transparent block (glass, slab) is placed on top of it.
 * If you are killed while having the chest GUI open and you transfer items from the chest to your inventory after you are killed, those items will be lost.

Dispensers

 * Unlike chests, when a dispenser is destroyed, the items inside are gone forever. Notch stated that this is a bug on Twitter.
 * The probability distribution is messed up, in what appears to be a typo-like bug. See the dispenser page and Get Satisfaction. The cause has been identified there, and a fixed implementation that additionally weights by stack size was posted.

Doors

 * If you place a door next to a Cactus it will break and drop them both, but the door will drop two doors instead of one as shown here. This can be reproduced indefinitely.
 * If a door is placed level with the cactus it will break the cactus and the bottom part of the door, leaving a collectible(see "cactus" above) but breakable window. This bug only occurs with wooden doors. 2011-05-12_18.01.28.png
 * When doors are placed, they are oriented such that they swing open out and to the left from the player. As such, if the right door of a planned double door is placed before the left one, both doors will swing the same direction.
 * Double doors may fail to protect a sleeping player, especially if there are already hostile mobs outside the house. This is presumably caused by the right door, which is somehow ignored by the game when searching for a way for a hostile mob to come in. This is supported by the fact that only skeletons and zombies attack the player, but never spiders, because they need a 2x2 space to get in.

Farmland

 * Tilled soil takes the same amount of time to destroy, no matter what tool is used.
 * Saplings can not be planted on tilled soil, however the ground under a planted sapling can be tilled.
 * Dirt can be tilled from any side of the block, even the bottom.

Fences

 * Occasionally, placed fences will become invisible under certain conditions: if there are no actual blocks within a pre-defined 16-block-high layer of a chunk, any fences placed within will be invisible. Stairs have the same problem.
 * When walking along (atop) a fence, no stepping noises can be heard. Once the player touches any other surface, all the steps taken along the fence will be played in rapid succession.

Fire

 * Fire has a South/West rule for applying damage. Placing a block directly above a fire prevents you from stepping into the fire and also makes it impossible to damage yourself by pressing against the block from the south or west sides. The north and east sides of the fire can still hurt you.
 * It is possible to have "Invisible Fire", fire that is dark and unlit.
 * A forest fire can cause strange patches of light to be left after all the fire has burnt out. This can be fixed by placing a new block on the center of the lit area.
 * If a block is placed directly above a burning netherrack, or any fire, and water is placed on that, it will constantly emit a hissing sound. Can be used to annoy players on SMP.
 * Numerous blocks are not flammable when they should be, including wooden stairs, wooden slabs, and fences.
 * When the player is on fire, and is viewed via the inventory window or f5, the fire sprite originates at their head. This results in fire hovering above the player.

Fishing Rod

 * When the line has been cast the fishing rod changes to a stick when it should have the reel at the base of the stick.
 * Fishing Rods can be stacked. Stacked fishing rods will assume the durability of the original fishing rod, thus allowing infinite uses.

Furnaces

 * When destroying a Furnace, unlike Chests, anything inside the Furnace will be permanently destroyed.
 * Furnaces emit light even if its face side is blocked. This is because the block itself emits the light, and it could be fixed by making the block in front of it emit light instead, but only if the block in front is transparent.
 * When you put coal + a smelting item in a furnace, then leave and re-enter the world, the fire icon glitches and will not shrink until the fuel source is about to run out.
 * The fire animation may not disappear even after the fuel is consumed.

Glass

 * Glass placed in the same block as an item entity will not displace said item.
 * While riding in a minecart, one can pass through a block of glass above the rail block. (These first two properties for glass also hold true for single slab blocks. These properties are suspected to be related to the blocks' transparency.)
 * When water is above glass, source blocks are never created.
 * If you attempt to light glass on fire, the durability of your flint and steel is lowered without any flames appearing.
 * Clouds seen through glass disappear during the breaking animation.
 * Glass placed next to downward-flowing water appears to increase the force.
 * When standing under glass during rain, the outside ambience for rain plays. Also, wolves play the shaking animation while under glass.
 * If a glass wall is placed next to TNT in water and you stand on the other side of the glass, you will always take only a half heart of damage.
 * Since it is transparent, glass placed next to a chest will not cause the chest's face to rotate where a normal block would.
 * Glass does not affect the orientation of double chests and furnaces.

Glowstone

 * When glowstone is placed at the upper limit of the map, (Layer 127), the side surfaces of the block exhibit the usual luminance but the top surface exhibits illuminance which is dependent upon the environmental lighting level,(i.e time of day or night). It is suspected that glowstone behaves like this anywhere it is against the edge of the "blockspace" or space where blocks are placeable, like the edges of a map beyond where any avatar has ventured and at layer 1, against the void.

Grass

 * Grass does not grow under signs or fences.
 * It appears that in arctic biomes, next to ice, grass can be generated underwater by the terrain generator.
 * Grass does not disappear if stairs or glass is placed on top.

Gravel or Sand

 * Gravel or sand will not fall down if it is placed above a non-solid block, like a torch or flower. If blocks of gravel or sand fall onto a non-solid block, they will accumulate into resources.Video
 * If you break a block below gravel or sand and are walking into gravel or sand, you will literally walk into the gravel or sand.
 * If you allow sand or gravel to fall on you, after moving around it is possible to be in such a position that you will not suffocate and you will be able to see through the sand or gravel and any blocks connected to the sand or gravel. This can reveal caverns.
 * If you place a sand or gravel block then quit the game before it starts falling, upon reload, it will float. If a nearby block updates, it will fall.
 * When sand or gravel is generated above a cave (or any opening), it will float until a space by it is modified in any way.
 * When sand or gravel is put above a boat, it will fall forever and act as "Quicksand"

GUI

 * When you open up the achievements interface at night, wherever in the sky there is not a cloud, the sky will be white.
 * While viewing the achievements interface, the world is not paused. Everything can move, as if opening the inventory.
 * The red glow featured at sunset and sunrise is normally a gradient. Pulling up the player's inventory will cause the gradient to solidify along a sharp boundary.
 * If you go from Windowed Mode into Fullscreen mode, dialogs are closed without evacuating items. Using F11 twice to close your inventory rather than ESC, allows the usage of personal crafting space for long term storage. Using the bug to close a furnace, dispenser, or crafting box will, allow the dialog to be opened twice thereby overwriting the previous one destroying any items placed inside. If one travels far enough away from the object without opening another dialog, the items will drop on the ground.
 * If you hit a movement key and at the same time open inventory or click that movement key will become "stuck". The same happens when you press the Alt-key while moving. Then when you click after releasing the movement key it'll be stuck, too. Pressing and releasing the same movement key again will stop you again.
 * If you disconnect from a server while a message is displayed, and then load a single player world, the text will appear in SSP as shown here.
 * If player takes a screenshot while crouching, (Left Shift and F2), the game will crash and the screen flickers.
 * In the debug menu (F3) the FPS counter shows Chunk Updates instead of FPS, usually while generating new chunks.
 * The debug menu may not be displayed properly when the GUI size is set to Auto.
 * Holding down or spamming right mouse button while holding down left mouse button will cause the "item action animation" to pause/stutter. The user is still able to mine, cut, etc while the animation has paused.
 * When clicking the 'Back to game' button, the click 'passes through' into the game, causing the player to unintentionally execute the left mouse button action.

Ice

 * After the Beta 1.5_01 update, Ice no longer regenerates when it is snowing.
 * Ice blocks do not have the slide effect on their border if no other ice block connects on them.

Ladder

 * Spiders can not climb a wall if a ladder is placed on the wall. (They get caught on the small edge of the ladder)
 * When it is raining, and if you are going down a ladder, the rain will stop moving, when obviously the rain is faster than your speed while descending from the ladder. It is unknown if this is a bug or not, although it doesn't look like it fits correctly.
 * Under certain conditions, if you are looking at a ladder, the selected block will toggle back and forth between the ladder and an adjacent block.
 * When holding shift, sometimes it is possible to drift as if you are on ice.

Lava

 * If the player moves into a corner to their southwest of which lava is on the other side, the player will be damaged(see South/West rule). This same bug can also incinerate items and other entities.
 * Lava can sometimes fail to generate proper lighting into the surrounding area, and will not damage the player. These pools can be traversed one layer without injury - submerging into the lava will cause the player to take damage, as well as force relighting of the pit.

Levers

 * Levers can be placed on the bottom of a block, as long as there is an open space, and a block horizontal to the open space. The lever will act as if placed on the horizontal block, but looks glitched, as shown [[Media:Brokenlever.png|here]].
 * Placing a lever on snow or glass or a torch will produce a similar effect.
 * Levers placed on slabs have a glitched model. 2011-05-12_17.45.34.png
 * Levers placed horizontally and facing North/South will not deliver power to surrounding blocks properly, whereas levers facing East/West will. With N/S levers power is only supplied to the four blocks on the same level as the lever and touching it. With E/W levers the four blocks level with and touching the block below the lever, and the block below that block, will also be powered.
 * A N/S lever placed between two note blocks lined up E/W will not fall if the block under it is destroyed, resulting in a floating lever.

Lighting

 * There is a lighting bug in which levels below 32 are lit, causing immense lag when loading chunks. This effects the Sky Lands map and the Far Lands.(Research on the bug The cause of the bug another topic confirming the lighting bug)
 * Smooth Lighting doesn't work when shadows are cast on water. Example
 * Smooth Lighting acts weird on certain blocks like signs, doors, and other special blocks
 * On some systems, nighttime can appear excessively dark (issue dates to approximately the Oct-Nov 2010). GetSatisfaction thread
 * From version 1.5 with smooth lighting OFF all stairs have complete darknes in the part of block where air is. This also renders bad into maps.(Stairs screenshot, Stairs on map)
 * In the Nether, after breaking glowstone, the area will start glowing again after some time. This results in light generated where the glowstone was alreay mined away.
 * Blocks placed above snow-covered grass cause the lower blocks to appear darker than they should, but only with smooth lighting.The Get Satisfaction page
 * There exists an underwater lightning problem which is most likely located at chunk borders. Example image...

Minecarts

 * Destroying a minecart while you are in makes half of your body sink into the ground. If the ground is only one block thick, you will fall through completely. If the minecart is on the bottom layer of bedrock, you will fall off the bottom of the world.
 * When spawning minecarts on a small track, they will gain momentum from colliding with each other.
 * Riding a minecart at the top of the map makes the player invisible until you leave the cart or ride downwards.
 * Sometimes minecarts disappear completely for no reason.
 * Riding a minecart into a Nether portal causes the game to crash and kills the player.
 * Minecarts can go off tracks or crash through the ground if their momentum is too high.
 * When exiting a minecart, if there is only a single block free above the track, the player will take some damage.
 * If you start sneaking right after destroying a minecart, you may crash and get buried, but there is also a chance you will get multiple minecart drops.
 * When exiting Minecarts when there is a block in front, the user may rarely glitch into the block directly underneath the Minecart and appear to be walking inside of that one block with the upper torso the only part showing until the user jumps out of the block.
 * If TNT is detonated near a minecart, it occasionally drops more than 1 minecart.
 * If 2 minecarts are put in a circular track, they will constantly bump into each other, accelerating. Very laggy in SMP.
 * A player/mob can be in a flaming minecart without taking damage or being set on fire themselves.
 * Water does not put out burning minecarts
 * If 2 minecarts on side-by-side tracks collide at an angle, they will both accelerate until they become disconnected. (This bug is the key component to making minecart Boosters)
 * If a minecart is dropped directly on top of another, they will combine into 1 cart, and accelerate twice as fast in a booster. More carts can be added for stronger boosting power.
 * When interacting with a Minecart+Chest or Minecart+Furnace while holding a useable item (e.g. filled bucket, bow and arrow, food), the item will be used when the chest is opened (bucket emptied, bow fired, food eaten).
 * Basic minecart rails do not sometimes connect together when they're placed.
 * Flowing water no longer affects minecarts as of a recent version.

Mobs

 * If a mob is riding a minecart and 2 or more mine carts get stuck in each other, after destroying or moving the carts away from the other carts the mobs will be invisible.
 * When up close to a Zombie Pigman, the inventory GUI will become much brighter.
 * Ghasts will shoot at the camera, not the player entity. This frequently causes fireballs to miss you in 1st person. The deviation is even larger in 3rd person view.
 * Squid still can't swim up in Beta 1.5_01; or perhaps they can't swim up again (according to Squid this was fixed in Beta 1.3).
 * Mobs can move briefly before map data is loaded when signing out and loading the world, usually resulting in the mobs getting stuck.
 * If a wolf is tamed when it's attacking another mob, it may still attack it when on sitting animation.
 * If a Tamed Wolf is left sitting when you exit the game and you return to the game in offline mode, the wolf will not respond to the command to stand up and follow.
 * Creepers who begin charging up and hide behind a wall, or out of sight of the player, will hold onto it's charge until it sees the player again. At this point, the creeper will resume either charging up or cancelling it's timer.
 * If you hit a pig with a saddle (by left-clicking) it will deal normal damage but it will also place the saddle on the pig. This can cause you to lose the saddle as you may accidently kill the pig, especially if you have wolves around.
 * If a creeper attempts to reach the character by running into a corner, and the block it is on is a ledge with no blocks on its level (or possibly above it), the creeper may stop as though it is hiding, then never move from that spot again unless the player breaks a block or moves the creeper to change these conditions. If the character moves to the other side, the creeper will randomly snap between staring at the player without moving and looking around as though it doesn't see the player.  If the player gets close enough it will still explode.
 * If a block is placed directly above the water, and a wolf swims against it, he gets stuck and suffocates unless the block is removed.
 * After getting out of water, wolves may shake themselves while jumping, or if told to sit, wolves will shake themselves in a sitting position.
 * Tamed wolves or any other mob, whether friendly, neutral or hostile, will not avoid harmful blocks, such as cacti, fire, or lava.
 * If a player descends from a cliff, a tamed wolf will jump off the cliff to get to the player regardless of height, rather than waiting to be teleported.

Paintings

 * Paintings can be placed inside snow.
 * If a painting is placed on a block with a fence on top, the painting may be 1x2 in size. This can not be removed without breaking the block or fence.
 * A broken painting will rarely drop 2 paintings.

Portals

 * Placing a boat in the portal and entering it will cause the game to crash.
 * Similarly, riding a minecart or a pig into a Nether portal will cause the game to crash.
 * Being killed in the Nether will cause chunks and a portal to be generated near your relative location on Earth, as though you had teleported back from the location at which you died normally.
 * Dying while in the Nether will also ignore a changed spawn point (via sleeping).
 * Opening the inventory then crafting while in a portal will destroy the item you are crafting and make the loading screen text turn gray, will add an identically gray "shadow" beneath the text, and will prevent the loading bar from filling. Everything will load as normal, though.
 * If the game is closed while entering The Nether, you will be sent to your spawn point on earth without held items, as if you were killed. However, it ignores a when the player's spawnpoint is changed via sleeping.
 * Portals over 2 km away from each other on Earth will link to the same portal in The Nether.
 * When returning from the nether in a portal it can sometimes spit you out in odd places miles from your original portal. example video(Originally spotted in Part 17, It switched again in part 18 (from the beach to a cave) then explored in part 19, finally dug to the surface, along with spotting the beach portal in part 20)

Pressure Plates

 * Wooden Pressure Plates are best mined with a pickaxe, not an axe. Destroying it with any other tool does not yield the plate.
 * Pressure plates (both wood and stone) have an odd fade to black gradient when smooth lighting is on.

Rails

 * If a powered rail is placed directly adjacent to a slope and the power source is a lever hidden in a hole in the wall, riding over that rail will cause both the minecart and the player to be teleported into the hole in the wall, causing suffocation damage or death.
 * If a rail is powered by a button that is directly above the rail and there is redstone wire leading from the block right behind the button, pressing the button causes the rail to be powered untill the rail is destroyed or redstone is connected to the rail.
 * Water that flows onto a powered rail destroys the rail, instead of returning it to item form like it does for normal rails.
 * More bugs at Powered Rail Bugs.
 * More bugs at Detector Rail Bugs.

Redstone

 * The particle color while destroying a redstone wire is grey (since Beta 1.3, because of dynamic colouring).
 * Some redstone circuits no longer work as they are supposed to such as T flip-flops (since Beta 1.5_01).

Redstone Repeaters

 * The particle effect while destroying a repeater are the same as pumpkins.
 * Cheated Redstone Repeaters (id 93 and 94) have the same texture as a double slab.
 * Redstone Repeaters don't always toggle correctly; when a circuit is switched on, some repeaters stay off and vice versa.
 * Can happen multiple times over the same circuit.
 * More likely to happen over longer distances.
 * Removing the Repeater and then replacing it will put it into the proper state, but the problem can come back at any time.

Sapling

 * If snow, fire, water, or lava are over a block, a sapling may be placed on that block even if it is not a dirt block. After a short time the sapling will recognize that it is illegally planted and uproot itself.
 * If flowing water hits a sapling, the item won't be dropped.
 * A tree can grow on top of a player, suffocating them.
 * If a sapling is planted at the top of the map, it will grow into a single wood block.
 * If a sapling is placed next to another sapling under low lighting conditions, both saplings will be turned to item form.

Sign

 * Placing a sign on top of a block at the maximum height removes the item from your inventory without creating a sign.


 * When placing a sign upon a block which is eight blocks higher than the level upon which the avatar is standing, requiring the use of the space bar to "jump and place", then the sign edit menu is activated whilst the avatar is in mid-jump. Upon exiting the sign edit menu the avatar continues to jump until the space bar is used again.

Sugar Cane

 * If a block is covered in snow, fire, water, or lava, sugar cane can be placed on that block violating the usual placement rules for sugar cane. When the sugar cane grows it will recognize that it is illegally planted and uproot itself leaving two loose sugar cane blocks.
 * Bugs in the terrain generation code can cause Sugar Cane to float. This is a purely visual bug. You can see the selection box when you look at it, and changing nearby terrain makes it show up.
 * Ghasts can not see you through sugar cane.
 * Arrows do not pass through Sugar Cane.
 * Sugar cane can be found growing taller than the 3-block height, but only naturally.

Snow

 * In snow biomes, water and lava lakes can generate below the snow and leave some of the snow floating. Players will fall through this floating snow.
 * Beds cannot be placed on snow.
 * Snowballs cannot be obtained when shoveling snow off of a sand block.

Stairs

 * Occasionally, placed stairs will become invisible under certain conditions: if there are no actual blocks within a pre-defined 16-block-high layer of a chunk, any stairs placed within will be invisible. Also happens to fences.
 * When smooth lighting is disabled, the inside faces of stair blocks (those not along the block boundary) may be improperly lit (usually far darker than the surrounding faces). This also causes item entities sitting on the inner step to be dark, while item entities on the top step are bright. This is due to the light value of the block being 0. [Example here]
 * The layering of the two cuboids forming the stairs in the inventory is wrong, rendering the backmost cuboid in front of the frontmost.

Slabs

 * When firing arrows at the opposite corner of the slab, your arrows may clip through and hit the block behind it.
 * Wooden slabs can currently only be properly collected with a pickaxe instead of an axe. This is caused by all 4 slabs using the same block id, with varying "damage" values.
 * Wooden, cobblestone and sandstone slabs all display the old slab particle when being mined.
 * When walking with 50-100% of your body over a slab, whilst being at the high of another block, the walking sound effect for the slab type will play, rather than the one which you are actually on.
 * A single slab cannot be made into a double slab if there is another solid block directly above the single slab.
 * Minecraft places the slab normally first, then realizes it's on top of another slab and combines them.
 * Torches, and other nonsolid items, can not be placed on single slabs.
 * It is impossible to be suffocated by single slabs.
 * With Smooth Lighting on, a slight amount of light can be seen passing through the sides of slabs. This does not affect mob spawning.
 * If a slab is placed on ice, it still has the "slippery" effect.
 * If half blocks are placed next to TNT, the damage is significantly reduced.
 * Neither single nor double slabs displace item entities.
 * When exiting and reentering the game while standing on a single slab with emty space below,you sometimes fall trough the slab.
 * When putting a slab on a slab which has another slab below it (or more) all slabs combine into one double slabs block, thus losing one (or more) slab in the process. (see example : http://www.youtube.com/watch?v=LIyYUaI0JHs)

Terrain Generation

 * Sometimes, the game may reset the seed that the map generates from. This is a result of tweaks of the seed and terrain generation code that are regular parts of the game's updates.
 * There's less ore (diamond, redstone, etc.) generated in any quadrant other than the South-West quadrant (+x, +z). This is due to a float --> int cast in the generation code, which rounds the numbers to zero instead of towards negative infinity, and causes a loss of ore when the value is negative. (Bug Report; discussion & solution; more statistical evidence)(Screenshots evidences -->1;2)
 * The "same chunk rotation bug" that has been solved in version 1.3 still exists for all caves in generated worlds. The solution to it should be similar to the terrain bug. Here is a screenshot from a world generated with version 1.3 with some of the most prominent chunk marked. (Here is the bug report on getsatisfaction.)
 * Large sections of "floating blocks" have been generated on new worlds for some clients. Here is a screenshot from a world in 1.5_01. The error only seems to appear in coastal areas in a large scale, floating blocks include: dirt, leaves and logs so far with select ores. Snow blocks seem also to appear on water.(Modifications within the screenshot have not shown bugs before and therefore I did not believe that they contributed to this bug.)
 * Very rarely, the map can generate a floating tree. This is due to a floating grass/dirt block in the air, with a tree growing on it.
 * Trees or Snow layers may generate above water/lava lakes, resulting in floating trees or snow layers. If you walk on one of those snow layers you will fall through it.

Tools

 * Axes do not break certain wooden blocks faster than hands, like you would expect. These blocks include wooden stairs, fences, wooden doors, signs, crafting tables and jukeboxes.
 * Shovels do not break farmland and soul sand faster than hands. (Soul sand is possibly intentional)



Water

 * Under certain circumstances, underwater players can breathe, and see through the water. An example is shown here(fixed in Beta 1.5_01)
 * Like lava, when water is touching the same corner as you it has a possibility of colliding with you, allowing you to float upwards. (South-West Rule)
 * Water sometimes doesn't flow into newly generated areas (usually when a cavern is being generated near a body of water).
 * Unlike Glass, other water blocks are invisible when viewed through a waterfall, even though there is air in between. Example.
 * Water source blocks do not regenerate over non-solid blocks such as glass or other water. Get Satisfaction: Water thats 2+ levels deep doesn't refill correctly.
 * Falling snow and rain can still be seen when the player is underwater.
 * When opening your inventory when swimming, you can only move left or right until you move.
 * Upon entering a newly generated map, water may be found floating in midair.

Weather

 * The Ambience sounds for rain do not play on Fast graphics.
 * Rain and snow falls underwater and in lava.
 * The outside ambience sound for rain plays while under glass.
 * Wolves get wet while under glass during rain.
 * When lightning strikes, ice, water, portals, rain, snow, and other particles behind it become see through.
 * You can sleep in a bed during a thunderstorm, even during the day.
 * When rain puts out a fire on Advanced OpenGL the area will sometimes stay lit.
 * Rain sometimes falls in snow biomes, and it sometimes snows in biomes other than Tundra/Taiga.
 * Sometimes rain and snow both fall at the same time in the same biome.
 * Rain and snow fall above the cloud layer.
 * Rain does not pass through signs.
 * If you open your inventory when it is raining or snowing, the sun will be visible.
 * The rain effect pauses when going down a ladder, but not up. Possibly whenever you are 'falling'.

Mac OS X

 * On some Mac OS X Systems, the World Select screen will not appear at all, making the game unplayable on those Mac systems.
 * In other cases, the Mojang AB logo will appear green and the title screen and the game in dark areas will appear red.
 * Since version 1.3, on some Mac OS X systems, when the player closes the game (clicks the X button on the window) the computer will freeze up completely. The mouse will still move, but nothing else responds, forcing a hard shut down and restart. In addition, the system does not acknowledge the issue (eg, no crash report window, no system.log entries). When on an afflicted computer, this rarely may not happen (often after a reboot or game update).
 * Afflicted systems seem to be older 32-bit Intel Macbook models, such as those made in and around 2007.
 * [GetSatisfaction ticket for this bug]
 * A work-around is to save to the title screen, and then Force-Quit Minecraft, instead of properly closing it.
 * Under MacOS X, Minecraft does not respond to either the Quit item in the Minecraft menu or it's shortcut, ⌘Q. This can be fixed by closing the window, then quitting Minecraft.
 * Pausing the game and expanding the window (+) as soon as the map is loaded causes a kernel panic, forcing you to restart the computer.
 * The game runs slow on Mac OS X 10.6 using a NVidia GeForce 320M graphics chip, however it runs with 60 or more FPS (average 120) on Ubuntu, using the same system.
 * Minecraft uses an 8-bit depth buffer on many macs, including brand-new high-end ones. This makes distant objects look terrible! It can be remedied by specifying the size of the depth buffer when creating the PixelFormat for the OpenGL context. Changing Display.create to Display.create(new PixelFormat.withDepthBits(32)) in net.minecraft.client.Minecraft.startGame fixes the problem. Look at this before and after screenshot and notice the huge difference.
 * On some Mac's, there is no audio, when you turn on the sound on Minecraft, the game hangs for a minute, then returns to normal, but still no audio.
 * Since a recent update (roughly on 5/1/2011) to MacBook Pro's (2011 model), there are patches of white in the sky on many users clients. Additionally, the health bars of items are white and the background to the inventory and options menus are completely white.  Also, when you sleep it becomes all white as well.  Force updating the client does nothing to help nor does updating your Java.
 * [GetSatisfaction ticket for this bug]

General

 * The input field of the multiplayer connect screen is too short for the input of IPv6 addresses and long domain names.
 * IPv6 literal addresses are not parsed properly. The code appears to split on : and pass the first array element as the address and the second as the port, so 2001:470:db8:42::1 becomes 0.0.7.209 port 470. (To be correct, it should treat the entire thing as an address if there's more than one :, unless of the form [2001:470:db8:42::1]:25565, in which case the contents of the square brackets are the address.)
 * If a player has respawned, he can place blocks on the block he is currently standing on. This will not decrease the block count in his inventory, effectively cloning blocks. This bug only occurs with non-opped players.
 * Full server world saves do not reliably save the entire world. This can be proven on a single person private server with whitelisting enabled when attempting to do a full server save via:
 * 1) Disabling incremental level saving with 'save-off' on on Minecraft console.
 * 2) Forcing a full save to disk with 'save-all' on on Minecraft console.
 * 3) Archiving and saving the archived world with 'tar -xvzf save.tg world' on shell in secondary system console.
 * 4) Turning back on incremental level saving by doing a 'save-on' on Minecraft console.
 * Enormous, cuboid areas (usually one or two chunks) of unfinished map open in random places. Caves, minerals, water, magma and mobs are visible when a Player peers into one of these voids. These areas cannot be walked on, causing a "[user] moved wrongly!" message to appear in the Server; however, players can ride minecarts through them with relative ease. If the void appears in the middle of water, Players can "float" over the void using a boat. Placing a torch next to one of these "void holes", dumping lava or water nearby, or disconnecting and reconnecting to the server will make the land inside of them reappear. These have become significantly less common since the 1.3 update.
 * When you sneak (in third person), your character's feet are "in" the ground.
 * Occasionally, the level.dat file is re-written, causing Minecraft to generate a new spawn. Also occurs in SSP.
 * Seemingly as of Beta 1.3, some players have been getting huge amounts of strange lag. They get good fps, but everything from placing blocks to damaging mobs can take anywhere from 10 seconds to 6 minutes. It is apparently related to the server, and NOT client-sided. The server recieves the data, but takes a long time to send it back out. It appears to only affect 1-2 people at a time, coming and going randomly.
 * As of Beta 1.5, this problem seems to be less severe, but still exists.


 * The minecraft server sends unnecessary many but small network packets. Between packets are often less then 0.00001 seconds. Tests have shown that if those packets get manually buffered that some players will have less lag and less disconnects. See this top 10 getsatisfaction problem report's user solution for more information.
 * A minecart track destroyed by water from above will disappear.
 * Using the /tp command to teleport to a distance individual can result in a lack of level data, causing a constant falling and then jumping of the camera.
 * Ambience sounds do not play in SMP.
 * You can cause a glitch whilst talking to other players, by holding down 2 or more keys at the exact same time. This causes the keys to go faster then normal to holding down one key. (Spammers use these methods)
 * The world data and the inventory of a player are not saved synchronously. If a player puts an item in a chest and the server crashes the item will be in the chest and the inventory of the player (duplicated).
 * Some players have issues where they can send information to a server fine, but have large amounts of lag when receiving information from the server. This results in SMP being unplayable for players who experience this bug.
 * Sometimes the client is slightly off on the position of other players, causing them to consistently appear slightly off of their actual position. This can cause players to "stand" inside of floors or walls.
 * When collecting a block/item on the ground, the icon in the inventory's hotbar does not distort for a short time.
 * Thrown snowballs and eggs have no effect on players, only on mobs.
 * Eating mushroom stew frequently doesn't return the bowl. The empty bowl is visible for a moment in your hand before vanishing.

Arrows

 * Arrows shot onto a wall cause the arrow to create a flickering wobbling repeat of the arrows movement. This happens mainly on glass.
 * Fired arrows will appear to come out backwards at first, then continue on a regular trajectory.
 * Many arrows fired appear glitched and stay in mid air, going back and forth, even if they hit a mob or another player.
 * A heavy arrow deathmatch causes severe lag on the server, takes minutes to recover. (picking up the arrows helps)

Beds

 * Sometimes when a player is sleeping and other player walks on that sleeping player the sleeping player will fall through the bed and the floor.
 * Trying to get into bed while sneaking disconnects the player(Illegal Stance).
 * If someone uses their bed in SMP, other players may get disconnected(Unrecognizable Packet ID: 17).
 * Attempting to hoe under a bed that would experience the monster spawning error would kick the player that used the hoe (illegal stance).
 * When right-clicking on a bed constantly before it is nightfall, the server may register that the player enters the bed, while the client believes the player is still not in the bed, causing the error message, "This bed is occupied," even when it appears there is no player inside. Other players will see the affected player moving around while he is in a sleeping pose.
 * The above "this bed is occupied" glitch sometimes also seems to occur if a player tries to enter a bed mid-jump.
 * If you try sleeping in a bed on SMP server while standing on it, it will start giving message "This bed is occupied" and you will be allowed to freely walk, but you will be really sleeping. Players will see you move but you will be lying down. You cannot trigger pressure plates while "sleepwalking", nor pick up items.

Boats

 * If you ride a boat over a chunk of water which did not load properly ( ex. the water is really there, but you can't see it and can see through the whole world ), the boat disappears.
 * When a Boat gets damaged (by a player), it does not shake.
 * If you see a player riding in a boat, it sometimes looks like they are running in the boat, rather than sitting.
 * If you exit a boat, you may get stuck standing on top of the boat, constantly falling and being reset by the server. This is similar to how fences used to act. You can get off the boat by getting out while it is moving, as the boat will slide out from under you and eventually allow you to fall into the water.
 * This may kick you from the server with message "flying not allowed"
 * The boat turns in intervals of about 10-20 degrees, making turning extremely difficult in tight spaces. In between intervals of turning, holding left or right will cause the boat to strafe left or right, respectively.

Compass

 * When spawning or crafting a compass in SMP it does not take you to your spawn, it creates a totally different 'north' example (Watch to the end for confirmation of original spawn)

Detector Rail

 * When placed immediately next to a track switch, will crash the server.

Dispensers

 * When a dispenser dispenses an item, there is no smoke puff and no sound is heard.

Doors

 * Doors opened and closed via redstone do not make a sound.
 * Doors opened and closed by other players do not make a sound.

Fire

 * It is difficult, if not impossible, to punch out fire on a block. It will simply re-appear a couple seconds later. This is especially noticable on Netherrack.

Furnaces

 * Furnaces can stop smelting items during a severe lag.
 * Furnaces occasionally turn to another direction after being placed. Appears to be random.

Jukeboxes

 * The records duplicate when you eject the record. Only one record can be picked up however, the rest are client-side duplicates.
 * When one player plays a music disc, other players can't hear it.
 * Setting a jukebox on fire when it is playing a disc may causes the game to crash.

Lightning

 * Lightning can strike inside houses and caves (is this naturally?). If lightning strikes you inside a cave you will catch on fire (no rain to put you out).
 * If Lightning strikes a painting, it causes a server exception and crash the server. (Caused by net.minecraft.server.EntityPainting.damageEntity)

Minecarts

 * Engines consume coal but do not move under their own power, making them useless.
 * Empty/Storage Minecarts start to behave strangely when they are too far away from the Player. They disappear completely, disappear until Players disconnect and reconnect, or suddenly stop on tracks despite having sufficient momentum.
 * Minecarts load before terrain sometimes causing them to be invisible until they are interacted with. Large transit systems and door water boosters are examples of when the issue occurs. (log out/in to reproduce).
 * Minecarts being destroyed do not wobble.
 * In smp, when you're trying to send a powered Minecart (with coal and a chest) to a destination that is far away, the minecart stops after a while and never reaches its destination. But if you approach the powered minecart, you can see it moving again : you have to stay close to it (chunk loading problem?)
 * An unpowered Powered Rail does not stop or even appear to slow down a Minecart when it is travelling very fast.
 * Three unpowered pieces in a row seems to stop it every time but frequently on the last piece.
 * If a mob spawns on a powered track circuit it will be pushed around it. example

Mobs, Hostile

 * Shooting animations (Ghast fireballs/opening mouth and eyes, Skeleton arrows) are not always visible. The sound of these actions (Ghast scream and Skeleton "twang") cannot be heard either.
 * Ghasts' fireballs occasionally do not explode, only lighting a small area on fire.
 * Sometimes mobs freeze in animation and can not be hit. They disappear after about 2 minutes. They are client-sided, so no other players will see them.
 * Some users are reporting mobs will be invisible, but can still attack you. On update 11/24/2010 SMP health update post Notch explained that to see invisible mobs, players must set their difficulty to the server side difficulty or higher.
 * This does not always fix the problem; on occasion, mobs will fail to load client-side.
 * Sometimes when the character dies, monsters will stay loaded client-side and not be loaded on the server side.
 * Sometimes players can hit mobs multiple times before the server registers the hit. The hits will then all register at once and the mob will be subjected to several knockbacks at once, flying into the air.
 * When a mob dies, its corpse sometimes sticks in the red death animation and doesn't despawn.
 * When slimes divide in SMP they may create client-side duplicates.
 * The lower half of mobs can not be hit with a melee weapon when you are 1-2 blocks below them. They can, however, be hit from directly underneath.
 * If escaping a Creeper and they do not explode, they will stay puffed up and explode imediantly after you get close enough, even after giving them the cool down time. While expanded, they act as though they are the size they look, allowing them to jump 2 block heights.
 * Slimes that deal damage spawn in the Peaceful difficulty.

Mobs, Passive

 * Squids can fly upwards.
 * When a pig is struck by lightning, you get client-side pig zombies that cannot be killed (in addition to the server-side one)
 * Copious amounts of tamed wolves in a concentrated area prevent the spawning of nearby passive mods (easily up to 10-chunk radius).
 * Occassionally after dyeing a sheep they will still yield wool in their original color (i.e. white).

Mobs, Friendly

 * Occasionally, Wolves can disappear on SMP Servers, Disconnecting and Reconnecting fixes this.
 * Sometimes after reconnecting to a server, wolves that were previously sitting will appear to be standing. They will still behave as though they are sitting.
 * Occassionally when wandering a significant distance from a sitting wolf, it to teleport to your location and become active.

Paintings

 * When copying an SSP world onto an SMP server, paintings are removed in the transition.
 * Paintings can be destroyed in spawn-protected areas.

Redstone

 * Since Beta 1.4, pulsars do not work, and many circuits have become glitchy in SMP.
 * Sometimes after waiting long enough (10-20 minutes?) a pulsar will start to work.
 * The particle colors for Delay/repeater blocks are the same of pumpkins.
 * The display of redstone differs from it's behavior when placing a block with torch on top next to a redstone wire (as well as on redstonewire-edges).
 * Giving redstone torches short pulses (via edge detection) causes them burn out, even if there is a pause > 5s between pulses
 * As well as repeaters, torches lock their state randomly when being wired for clock generating
 * While destroying a block, quickly applying redstone repeatedly will cause you to see textures of different blocks.
 * Redstone Repeaters occassionally become locked if their chunk becomes inactive while they are in their "on" state.
 * Occassionally Redstone does not properly turn on/off when you remove/add the block powering it (http://getsatisfaction.com/mojang/topics/smp_repeater_bug?topic_tools=open)

Signs

 * When a sign is placed in multiplayer and text is entered (but not finalized), and a torch is placed within 10 blocks of the player who placed the sign (not the sign, but the player), the entered text disappears. Interestingly, when a torch is placed within 10 blocks of the sign placing player BEFORE the sign is placed, any subsequent text entered will not be erased by torches placed OUTSIDE the radius of the first torch, but text will be erased by torches placed INSIDE the radius of the first torch. Oddly, this behavior only seems to occur with torches, though these tests were not exhaustive of the minecraft block set, and further work should be done to verify this claim.

Time
using a bed to change time does not affect the clock generators. Restarting server fixes it quickly.
 * The server command /time breaks 'clock based' circuits

TNT

 * A TNT block meant to drop will enter a repeating fall animation (but not actually fall) when lit.
 * A TNT block can also explode twice, but this will not damage the environment twice.
 * If a lot of TNT is lit, some TNT may explode but leave behind an image of an exploding TNT block that is almost completely white, and will hover in mid-air while repeating the falling animation. The ghost TNT will not disappear unless the player disconnects and reconnects. (This is a client-side TNT entity)
 * Too much TNT detonating at once will freeze the client, often requiring the game to be closed. Though the client freezes, the server has just a short peak of CPU usage, which results in no noticeable lag in other areas most likely due to particle invisibility and/or the nonactive chunks.
 * There is no limit for TNT explosion particles which kills/freezes the client.
 * The explosion result differs between client for ~5 seconds, as soon as the chunks update, the serverside calculated explosion will be shown.

Trees

 * Trees that have grown recently, especially packed together in a tree farm, sometimes don't update the client with the leaf positions. This creates "invisible" leaves that the player can't walk through and makes navigating tree farms an annoyance.
 * Using bone meal to quick-grow trees will sometimes cause "floating" trees to grow with the sapling still at the base. Removing the sapling or using more bone meal can cause the tree to grow into an enormous bundle of leaves with no log base. These leaves will now respawn immediately after being harvested. The only way to remove these glitched leaf blocks is to burn each block individually (fire will not spread for some reason) OR set the floor below the leaves on fire OR build an umbrella above it, the shadow seems to instantly vanquish the leaves. - This glitch is vastly more common when quick-growing trees under another trees foliage. Again, disconnecting and reconnecting will reset these "ghost trees."
 * Planting a sapling and waiting a bit will sometimes yield tree trunks with weird distributions of leaves, and in some cases, no leaves at all. Trees can also grow but be invisible, making it impossible to traverse a tree farm after a while. Rejoining the server appears to make invisible trees visible again and fire will swiftly cause phantom foliage to be made manifest. You can also place a torch to make the phantom foliage appear.
 * Leaves from trees will overwrite some blocks, such as a nearby fence. This is problematic when it renders areas previously thought safe accessible to hostile mobs.
 * Placing a torch on Leaves does not make the 'pop' sound for the item being placed.
 * Birch saplings will not grow in underground tree farms, even though there is proper lighting.

Tools

 * The last use of any tool causes a block to not drop, unless you normally get a drop from using your hands.

Water

 * You may find yourself drowning despite having a full breath meter. This is caused by the client registering that the player has gotten air, but the server registers that the player is still underwater. This causes the non-synced breath meter.
 * In some underwater areas there are lines of lighter spots at the bottom the water, likely on the edge of chunks where the next chunk over used to be empty space (causing light from the side to reach the bottom on the edge of the chunk)

General

 * Occasionally, the level.dat file is re-written, causing you to lose your held items, and generate a new spawn.
 * Sometimes you can see through everything; this randomly happens on all games on all platforms. Toggling the fog distance will change everything back to normal (Default key is F).
 * The biome triangles grasscolor.png and foliagecolor.png are ignored when included in texture packs.

Achievements

 * The achievements "Time to Farm!" and "Time to Strike!" requires a wooden hoe and sword (respectively), despite the description not specifying and the player being able to build stone or better versions of these tools.
 * Throwing leather on the ground earns the achievement for killing a cow.
 * If creepers blow up a tree and you collect the wood, or someone tosses you on SMP a block of wood, you'll still get the "Getting Wood" achievement.
 * Achievements (& stats?) saved when playing offline and achievements saved when logged into Minecraft.net are separate and do not sync.

Beds

 * Depending on the placement of a bed monsters will spawn on or near the bed regardless of light level. Sometimes this can occur even if the bed isn't touching any walls.

Doors

 * If you close a door on yourself and jump, you can stand on the lower half of the door. This can be used to climb on top of doors.

GUI

 * You are unable to directly swap items in your inventory if the two items are same. This is important if you would like to swap the same item type with two different durability values. This is a result of the way combining stacks works.
 * If you enter Fullscreen mode, then exit it, mouse clicks will no longer work for game dialogs (game menu, inventory etc.). However, mining and using items still work. Pressing Esc, waiting for the game to save and restarting the client or re-entering fullscreen to save and quit resolves this problem. Here is a topic on Minecraft Forums related to this bug.
 * If a player enters a world, toggles debug mode (F3), then exits the world with debug mode still on, debug mode will still show.

Lava

 * Sometimes, lava won't cause damage. More common in SMP.
 * Sometimes, a lava flow does not stop flowing when its source is removed.

Lighting

 * Occasionally, some chunks of the map do not update with the day/night cycle, as seen here. Also, even in caves or closed environments the player can still see lighting bugs, (i.e. An area has full light and it has a small spot of full darkness next to it. When the spot is edited, it changes to normal.) These glitches are fairly common and can cause multiple problems. Usually waiting for a moment will fix this or you can simply toggle the fog.

Mobs

 * Zombies and Skeletons may spawn in well lit areas while you use the bed to sleep.
 * Creepers may spawn in open areas with torchlight.
 * Squid can spawn in unintended locations, such as from cavern springs. This is more common in multiplayer.
 * Tamed Wolves will attack you if you shoot yourself with an arrow. This can be achieved by looking straight up, shooting an arrow, and moving forward a small bit to compensate for a small amount of curve. Another way is to shoot an arrow at the ceiling and stand directly under it and destroy the block the arrow is on. This will cause the arrow to drop and hit you.
 * Sometimes a tamed wolf may get stuck in the wall, causing it to slowly die. You can save him by breaking the block he is stuck in.
 * If you are riding a pig, and it walks into a low room that is not low enough for your head to be in the ceiling, you may start suffocating.
 * Wolves are known to stand up from their seated position randomly, and teleport to the player even though he is a large distance away. You may have to travel back all the way in order to put the wolf back in its place.
 * Squids do not despawn as of Beta 1.5, but slimes seem to despawn now.
 * Other players footsteps, block breaking/placing sounds, bow sounds cannot be heard. The "mining progress" texture cannot be seen by other players too, and the animation when mining a block isn't correct. (as compared to swinging in the air)

Paintings

 * A painting placed over a light source does not block the light.
 * Paintings do not use the smooth lighting, even if all blocks around it do.

Redstone Repeaters

 * A repeater will freeze upon save and reload of a world.

Score

 * When the player dies, their score is displayed as '&e0'

Weather

 * Thunder sounds play even at bedrock.
 * Clouds pass through solid blocks and can enter sealed off areas.