Yeah, I had this problem. Had 10 little problems, as a matter of fact. I zapped them all with `markfordelete, but now he's back. At least there's only one of him for now.

If you're tired of watching them mill around, that's one way to take care of it, but it's not permanent.
My second game, I just killed the bastard during the quest. Got a nice horse out of the deal.