I'm not certain, but I think that corpses only go *poof* when the mob dies and the thing you've
been charming to kill it is not currently charmed. They check to see who did the most damage,
and since the thing that did the most is an unaligned NPC, *poof*.

It's happened to me a couple of times, and only when I was in a group who were fighting the
"other, soon to be dead" mob.

Jyzan