This page's purpose is to list all the bugs players have come across. Most of the single-player bugs also apply to multi-player.
Survival Single Player (SSP)
General
A glitch has been observed where, occasionally, a given area of blocks can revert to their original state, partially or completely undoing any construction or mining that had been done in that area. Usually this happens after a long excursion into one of the natural cave systems.
Seemingly related to the above glitch is one where a specific chunk will constantly revert. In chunks that constantly revert, water will not duplicate if it is flowing, and water tends to linger much like lava when the source is removed.
You are unable to directly swap items in your inventory when the two items are same. This is important if you would like to swap similar items with different durabilities.
Sometimes you can see through everything and it happens on all your games. Toggle the fog distance and everything will change back to normal (Default key is F).
Iron bars and saplings may not appear in the inventory when collected.
If you wait a lot of time after map chunks are generated and then continue forward causing the game to generate new map chunks, the game will generate weird structures which do not connect properly with the map. Sometimes even creating mountains which are, in a sense, cut in half. Furthermore, if one chunk ends in an ocean, and the other starts off with land with an underground cave in it, the water will not enter the cave.
When destroying a Furnace, unlike Chests, anything inside the Furnace will be permanently destroyed.
When sand is generated above a cave (or any opening), it will float until a space by it is modified in any way.
Sneaking does not prevent the player from falling off of Steps or Slow Sand.
Sneaking prevents movement onto Slow Sand from any other block.
Since the November 10th update, there have been several performance issues in SSP. Save/load times have increased, sudden random FPS drops, and random crashing/freezing. It is unknown if it's just the patch and/or updated mods that cause it.
Occasionally, when saving the game and reloading, you will fall through the block you were standing on.
If you open a chest whilst at the same time as pressing a movement key, your character will continuously move in that direction until you open a chest again. This is also fixed by pressing the same movement key after leaving the chest menu.
Chests sometimes revert contents to a previous configuration. Opening a chest, modifying the content, exiting the game and then going back in, displays the items the chest had when it was first accessed. This causes newly placed items to be lost and removed items to be duplicated.
If you open a chest while teleporting, you can remove the items to your inventory after your arrival. When you go back, the items will be in the chest and your inventory. Video here: http://www.youtube.com/watch?v=j36xL-Xo11w
If doors are placed next to two stapled cactus-blocks, the door will immediately get destroyed and will drop two doors instead of one. One door can not be collected. If a door is placed next to two stapled and newly planted(small) cactuses, an uncollectable door will be dropped, and a door window frame will remain, which drops nothing.
Inserting a record and removing it before the song ends will cause the jukebox to eject a duplicate. Only one of the records will be retrievable, but the second will remain stuck in the world and eventually disappear after a certain amount of time. It is possible to abuse this bug to spawn hundreds of records.
When spawning mine carts on a small track, they will gain momentum from colliding with each other.
Having too many minecarts will cause the game to crash.
It is possible to gain neverending speed for a mine cart from abusing the bug by spawning many carts on a small track.
Riding in a minecart on above track may cause your player's image to disappear until you die or reopen Minecraft.
Sometimes moving minecarts disappear completely.
If you open your inventory while in a minecart, your player hand model will not function as expected.
Riding a minecart into a Nether portal causes you to become stuck.
Removing a minecart while riding in it will cause you to go through the ground, but only if the track is sitting on a block and air is all around it.
If a minecart enters lava, the client will freeze. If the player is in the minecart when it enters lava, the client will crash.
If you make a cannon that can fire a lot of TNT and then place a single track facing away from the cannon on the "firing spot" (the place where you put the TNT missile), put a minecart on that track and detonate the TNT while in the minecart, you will fly up into the air (if you have god mode on) and when you come back, you will find more than one minecart item near the cannon. This has only been proved in version 1.2.2 and before, I have yet to test if it is still true.
If a mob is riding a mine cart 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 Pig, the inventory GUI will become much brighter. It is unknown if this applies to any other mobs, or varies in the mac/linux versions, or if it's present in SMP.
If you stand still, ghast will shoot fireballs over your head, without damaging you, unless they are directly in front of you, if you can get to their height, or if they are directly above you.
If a painting is placed and immediately removed, there is a chance that the picture frame will get duplicated.
If a block is removed from behind a painting, it will pop off the wall when a player touches it after a reload, even if it is a multi-block painting and there are other blocks still behind it.
Placing a boat in the portal and entering it will cause the game to skip the "safe area" finding algorithm. This means that you will appear in the Nether world exactly where you are meant to regardless of blocks in the way. Example video.
Being killed in the Nether will cause a portal to be generated near your relative location on Earth, as though you had teleported back from your "final resting place" normally.
Riding a minecart into a Nether portal causes you to become stuck.
While underwater, you are able to place blocks at the location of the player.
(To clarify this a bit, on the surface, you are blocked from placing a block on yourself, underwater, this blocking does not exist).
It is possible for multiple water currents to crash against each other and create an inescapable rip-tide. Not only will this rip tide hold you in one place, it will also throw you from a boat if you are sailing it.
World Select
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 Specifications will appear green and the title screen and the game in dark areas will appear red.
In dark areas some sides of tile blocks will not render making a see through cave and grass in daylight will appear purple, water in darkness will also not render. This has only been proved with Mac OSX "Tiger."
Once the player has entered The Nether, the save file will appear as 0.0 MB (or something similar).
Relating to the above glitch, some worlds will have negative file sizes (such as -0.02 MB).
Survival Multiplayer (SMP)
General
When being hurt, the player won't make a sound.
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.
If a player dies and disconnects without respawning, upon rejoining, they will be invisible and invulnerable to damage. Items cannot be picked up by the player, nor can hostile mobs hurt them. Entering a minecart will crash their client. A heavy-handed workaround is to delete the players .dat file from the world/players folder. A more elegant solution is to have the player log off and use a program like [NBTEdit] to edit their health to a positive value. If their health is 0 or lower they will be in this "ghosted" state.
Crouching is not visible to other 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:
Disabling incremental level saving with 'save-off' on on minecraft console.
Forcing a full save to disk with 'save-all' on on minecraft console.
Archiving and saving the archived world with 'tar -xvzf save.tg world' on shell in secondary system console.
Turning back on incremental level saving by doing a 'save-on' on minecraft console.
If a player attempts to use a Golden Apple and the player's cursor is aimed at a block, a minecart track will be laid where the cursor was aimed.
Walking over an arrow that has been shot will stay planted of the ground but will add arrows to the inventory. The entire inventory of a player will be filled with arrows up just by standing on an arrow.
Arrows bounce off mobs, dealing no damage
Arrows can only be seen by the player who shoots them.
You cannot see any arrows that a skeleton shoots or the shooting sound they make. They still can hurt you.
Destroying a chest will spill its contents and every item in the chest will be duplicated. Only half of the items visible to the player can be picked up, so no items are gained nor lost in the process.
Quickly clicking on items and moving them around can cause them to disappear from your inventory and in some cases, to be duplicated.
The duplication seems to be caused by a server/client sync error. When holding the item place it and then quickly pick it up. Notice that the item with flash again in the bin location where you just put it. It seems the server is sending back that the item is still there after you have picked it up. While the 'ghost' item is shown in the bin placing the item in your hand will cause the item to be duplicated. In the case of stacks it will double the stack and in the case of un-stackable items it will remain in your hand (mouse) and also in the bin.
The disappearing seems to be caused by the same bug just in the opposite way. Instead of the server lagging behind the client and telling it that the item is still there the server will erroneously delete.
Coal can smelt 8 items per lump. However, in some cases, smelting a multiple of 8 items will use up all the coal, but leave one item without smelting. When cooking Pork, the furnace will not take any more coal after having burnt the first lump. The player has to close the furnace window and reopen it to continue cooking. The furnace will continue to show the fire animation after this, even when empty. Also, the animations in the furnace window (arrow showing progress, fire icon when consuming the fuel) seem to be broken as well.
Furnace progress bar is not working.
If a player moves too far away from a furnace while items are inside, all items will be lost.
The last inventory slot (bottom right) is overwritten by the active hand slot on logout/login; this is caused by an array-length error in the server code.
Shooting animations (Ghast fireballs, Skeleton arrows) are not visible and don't play any sounds.
The Ghasts' fireballs occasionally do not explode, only lighting a small area on fire.
Zombie Pigmen do not attack when hit. This is most likely due to the invincibility glitch.
Sometimes spiders freeze in animation and can not be hit. They disappear after about 2 minutes.
Some mobs are invisible. A scenario would be that a Creeper explodes next to you, making no sound and dealing you no damage but damaging the ground.
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.
In addition to not triggering doors, stone buttons may jump from the wall they are actually placed on to the one opposite upon being pressed the first time if there is just one block of air in between. They can then not be removed reliably without also removing the block to which they are attached.
Some swords do not seem to be doing the correct amount of damage. Mobs take a very large number of hits to kill using a weapon, and while reach does seem extended, it's probable they are dealing unarmed damage.
Dropping them (i.e., by pressing Q while holding them) and picking them back up will revert their damage to zero. This probably is related to the player and mob server-side health issue. Applies to all items that take damage (e.g.: Armor).
Planting a sapling and waiting a bit will 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. Trees with "weird leaves" cannot be cut down, as they regenerate instead of yielding wood blocks.
Foliage from trees will overwrite some blocks(such as a nearby fence)
Placing a torch on foliage does not decrement your inventory. It also does not make the 'pop' sound for the item being placed. You can subsequently destroy the torch and collect the item, giving you a source of infinite torches.
Foliage does not fall when the tree has been cut down.
Monsters are spawning on top of trees, making tree farms very dangerous.
To a player, it will appear that some seeds cannot be picked up. But to the other players, these seeds will be invisible. Hoeing the ground directly beneath you improves the chances of harvesting the seeds. Disconnecting and reconnecting will leave visible only those seeds which are actually able to be picked up.
Crouching/Sneaking over tilled soil does not prevent it from becoming trampled. Same goes for planted seeds, etc.
Whenever you enter a boat you will greatly increase in lag.
If you ride a boat over a chunk which did not load properly ( ie, the water is really there, but you can't see it and can see through the whole world ), the boat disappears.
You can ride boats onto land, and very slowly move. ( example: place a water source on the ground, put a boat on it, and hop in. You can ride off of the water. )