What I expected to happen was...:
Mobs glitchedin walls not dying when I launch the world in the new snapshot.

What actually happened was...:
All mobs glitched in walls (like when you made spawn too many chickens in a little hole) instantly died at the launch of the map.

Steps to Reproduce:
1. Create a random map (not in 14w06a), dig a hole, make spawn a lot of mobs, to be sure some of them are pushed in the walls.
2. Upgrade your game to snapshot 14w06a
3. Join the world and see all the mobs glitched actually died.