I've seen this a few times, but I haven't done many dungeons yet to experiment. Sometimes a random guy just runs off like she's been feared. I think they are randomly losing the target and thus running off like it's a dead target because re-interacting doesn't work.

For now I've just stuck a macro for /jamba-follow master melee next to my DPS key. I'm going to do a little more dungeon running and probably add /target party1 to that macro if it is indeed acting just like a fear and they are losing the target.