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My Gamerscore has gone up, but I can't find the actual acheivement other than when I'm on the game itself. It doesn't seem to record the fact that I played the game, just the points for the acheivement.
On a couple of sites that get feed from XBL for my GS reflects the increase. I haven't checked highscores tho.
I turned my system all the way off and back on again and I still have the extra acheivement points