Java Edition 15w46a

15w46a is the fortieth snapshot released for 1.9.

Boats

 * Boats travel slightly faster than before.
 * Banners and signs
 * Now replace replaceable blocks such as grass, instead of trying (and failing) to be placed on them.
 * Experience
 * Now is collected at the middle rather than at the head
 * This means that if a large amount of experience is collected, it will no longer block the player's view.
 * Blocks no longer drop XP when the  gamerule is false.
 * Farmland
 * Mobs smaller than 0.512 cubic blocks can no longer turn farmland to dirt by jumping or falling on it.
 * This includes rabbits, chickens, bats, ocelots, wolves, cave spiders, endermites, silverfish, small slimes, small magma cubes, and all current baby mobs.
 * Filled buckets
 * Now replace single snow layers when on the top, instead of placing the water or lava in the air above the snow layer.
 * Iron bars
 * Texture of a side-ways oriented bar now includes an edge texture.
 * Iron golems
 * Iron golems spawned in 15w46a and later have 100% knockback resistance.
 * Mob spawning
 * Mobs can no longer spawn inside blocks that block movement but are transparent, such as leaves.
 * Mobs can no longer spawn in blocks containing rails, powered rails, detector rails, or activator rails.
 * Mobs can no longer spawn in blocks containing buttons, tripwire hooks, pressure plates, levers, redstone torches, redstone repeaters, comparators, or redstone dust.
 * Ocean monuments
 * Now require a 16 block square radius of deep ocean, not just a single deep ocean block at the center.
 * Rabbits
 * Smaller than before.
 * Chance to drop a rabbit's foot is now 10% + 3 percentage points per level of Looting (was 2.5% + 1 percentage point per Looting).
 * Now only spawn in deserts, flower forests, taiga, mega taiga, cold taiga, ice plains, ice mountains, ice plains spikes, and "hills" and "M" variants of these biomes. Even in these biomes, spawn chance is somewhat reduced (weight 4 out of 44–52 rather than 10 out of 50–58).
 * Rabbits are faster when panicking.
 * Rabbits no longer prefer begging for food to mating.
 * Non-killer rabbits now avoid players within 8 blocks and most hostile mobs within 4 blocks (except slimes, magma cubes, and ghasts), and move faster when doing so. Also, avoidance range for wolves was reduced from 16 to 10 blocks.
 * Health reduced from to.
 * Naturally-spawned rabbit's skin depends on the biome. When breeding rabbits, there is a 5% chance the baby will match the biome rather than either parent.
 * In a snowy biome, 80% white and 20% black & white.
 * In a desert or desert hills, 100% gold.
 * Otherwise, 50% brown, 40% salt & pepper, 10% black.
 * MoreCarrotTicks no longer has any effect.
 * When destroying crops, MoreCarrotTicks is set to 40 rather than 100.
 * Rabbits eating carrot crops now reduces the growth stage by 1 level, only removing the crop block entirely if the growth stage was 0.
 * Rails
 * Powered rails and activator rails now transmit power to each other.
 * Redstone
 * Hitbox for redstone is now smaller based on the connections, similarly to fences
 * Snow Golems
 * No longer leave a trail of snow if the game rule  is false.
 * Wolves
 * Collar when tamed is now red, as it had been in releases before 1.8, rather than orange.