In 12w04a zombies try to stop themselves from burning up In daylight
this appears to no longer happen they will make no attempt to stop themselves from burning up in sunlight unlike skeletons

Steps to reproduce
1. Create an superflat world
2. Put some water down using an water bucket
3. Spawn an zombie and skeleton next to the water using an spawn egg
4. The zombie will not to go into the water to stop itself from burning up in sunlight unlike the skeleton