Oh, sorry to doublepost, but I did notice that he doesn't seem to want to rejoin the group unless the pc apologizes for something. Is that the mod in play? I don't tend to bring him along much at all so I don't remember if that's standard for him or not.
I can't help you with the stutter bug, but apologizing to get him back into the party is standard behaviour, not the mod. I was surprised too the first time I played.