I was fighting with brigands together with another mercenary company. When one of mercenaries struck a bandit with 3 headed flail, game froze for a second or two and then crashed with some error message (sorry I didn’t save it. ((( ). However, the same guy managed to hit another bandit with said flail in previous round or so no problem.
So, maybe you should check how 3 headed flail is implemented in the code once more or something?
Sorry if that wasn’t much of a help.