Minecraft wiki entry for Development_versions, associated text: Fixed the wither's starting explosion not being disabled by the mobGriefing gamerule[18]
Fixed a few crash bugs related to world generation, map item expansion, and other things.
Reverted previous lighting changes, which corrected such bugs as:
The Nether being extremely CPU intensive.
Map generation taking extremely long.
Fixed mob AI considering cobblestone walls as blocks of normal height.
Fixed a few texture oddities with the witch.
Fixed entities in water producing glitchy water sound.
Gaining multiple levels at a time will no longer play the leveling up sound over itself as many times as leveled.
Fixed the "A 64 bit Java installation is recommended for 'Far' render distance (you have 32 bit)" message being covered by the bottom 2 buttons.
Fixed pets teleporting around randomly.[19]
Fixed being unable to place paintings larger than 1x2 and them popping off if they have been placed before.
Fixed destroying blocks under you with Efficiency-enchanted gear.
Fixed potion spawners crashing the game.[20]