When my pet wolf kills a zombie, it crashes the game...

Entity Type: Wolf (wg)
...
Entity's Vehicle: ~_ERROR~ NullPointerException: null

How to reproduce:
1) Make sure your pet wolf is up and ready (not sitting).
2) Whack a zombie.
3) Watch your pet go after the zombie.
4) When the zombie dies, the game crashes.

See attached crash report file for details.

I haven't tested to see if my wolf killing other baddies will crash the game, but killing passive mobs (sheep, cows, etc) doesn't seem to bother the game.