This has happend several times at 20+ waves now, so, I thought Id QQ and make a screen shot. Its like the game just decides hes dead before hes dead or something =s
Yup, had this happen a few times. Not with GS though as it was with Discipline. NPCs could be at 10-30% health and would just decide they had had enough. Also had problems where Chomp is applied and deals damage regardless of shields being up.
Both these issues felt more prevalent in MoP and I've only noticed them very irregularly in WoD. Good luck reaching 30 by the way!