Why do mobs get fat when you kill them? These are mobs, not hot dogs. They aren't supposed to plump when you kill them.
This isn't a bug, but an annoyance. Some of the death animations of certain types of mobs are just too darn long. Certain types hit the floor and you can loot them, others throw a William Schatner-esque fit on the ground before you can loot them. Seriously, tell the mobs to stop overacting and let me loot them already. lol