Heh, perhaps as the DM in question I should give a reply too
Yeah, the problem has appeared for a while. Things didn't look all that bad at the start (They started out as slaves, but managed to slay their overseer and seek freedom. Even when the opportunity arised, they looked at the player in question, asking if it's a good idea to slay him), but they're becoming more and more like sheep that flock after their herder (The cohort part is very true and would actually apply to more players). Especially the last few sessions have become a problem.
'NewbyDM' did receive more XP at the start of the game for better roleplaying and coming up with ideas on his own, but add to that that he was present at all sessions and didn't get himself killed in various stupedious ways, he now is 2-3 levels higher than the rest of the party, so further XP penalties would be rather bad. In fact, he's currently receiving less XP because he's fighting opponents less powerfull in comparison to himself and because he puts himself less at risk.
The player would have to do a lot to get disfavored by the party. By now he could probably get away with dominating the partymembers one by one, stripping them off their magical items and then take the items for himself.
The party is currently on the road, avoiding contact with practically all other travellers (this has it's reasons... the roads are currently pretty deadly), but when they reach the next major city, I'll have some NPC's asking them to do some individual tasks, but I'm just afraid they'll run to him asking for step-by-step instructions on how to do that.

Perhaps I would just have to make him unaccessable at that time
