Assist command

Sorry I don't have a log or a very good bug report but over a number of characters I've had trouble with the assist command. Most recently, it was me and a shapeshifter in cobra form fighting the multi-headed dragon in arboria. When I tried to assist it would say: "You assist the cobra against the dragon" They aren't here" One other occasion I can remember with another character, we were in the arial city fighting battlement guards, I used the assist command and wound up bringing in a guard that they weren't fighting. I think I may have been hitting the second guard or something while they were hitting the first.