Seems to be bugged in the "Widowmaker" quest. As soon as he gets near the witch, he is constantly aggroed on me. Stopcombat won't stop him, neither will my (admittedly weak) calm spell. The only way to stop him is to kill him, thus failing the quest. Even if I don't enter the fight, he will always attack me. I've tried killing her with "kill", but as soon as I get near the body, he attacks me. I even tried casting a ranged spell to get her to come to me, but he still attacks me as soon as she gets near. Quest seems uncompletable (not a word) at this point.
I was able to complete the quest by paralyzing him, killing the witch, looting the axe, and running back and handing it to him. So, it's clearly the part of the script that makes him attack the witch - instead of making him attack her, I'm guessing it just makes him hostile to everything.