Ok, these are all wild speculations, since I'm running out of ideas and I don't have the replay to examine it in detail.
I notice that the warlock who shares the square with him had astral shield on. I guess it shouldn't make a difference though, since demonbred wasn't beating him, unless he somehow got enslaved or something similar (I don't know whether unholy command works on demons). Did warlock by any chance cast stellar cascades somewhere in the vicinity? What was warlock's random pick? Water?
Also, did any of his buddies have death magic? That is, were any of these spells cast: rigor mortis, soul vortex, ghost grip (although GG should only work on enemies)?
I'm not even sure that all these spells can result in anything like what you experienced, but maybe they could.
Btw, if you don't want to look at the replay again, I'm not forcing you. I just want to help (apart from being curious why it happened, of course).
