I just replaced my munched 2006 X7 rear derailleur with a new 2007 one, and something isn't right. The whole thing feels loose and weird when I mount it up.

Thing is, the big hollow hex bolt that connects the RD to the hangar is loose- it slides inside the RD body maybe 1mm, just enough to be noticeable. It's like the bolt is too long by just a hair. On my old busted one, the bolt is solid and does not move at all.

Feels fine with a chain on it. Am I worried over nothing? Is it supposed to do that?