I was remembering a different bug board post, where it was a person outside the group that got hit. http://forums.carrionfields.com/dc/dcboard.php?az=show_mesg&forum=17&topic_id=21228&mesg_id=21228&listing_type=search

I have seen a scenario where the targeting logic broke and an NPC actually attacked a different NPC in the room that was just sitting there, I think it had to do with my merc being in the room. I think I logged it, I'll see if I can post it for you.