13w06a: Rare Baby Animal hitbox bug, grows up to die by suffocating itself in a wall

(Affects Snapshot 12w06a, Mojira wouldn't recognize) Sometimes, in one session of Minecraft, if you breed an animal (cow), the baby has an incorrect hitbox when it grows up, resulting in it suffocating itself in a wall. Restarting Minecraft fixes it, have not been able to replicate since.