Avast! found this today while power levelling me skinning. OK so if you got cold blood and mutilate then good...if not then go respec :P
OK so basicly there's a bug with cold blood so that if your target only has enough HP for ONE dagger crit then it will only attack with one dagger. And there lies the bug! if your mutilate only hits with one dagger then cold blood is NOT used but it DOES crit! OK this sounds confusing so here's a video!
http://www.youtube.com/watch?v=DesLoGWsyWE