hmmm, beats me.
the only ways to get AA is by either forcing it or let the game handle it.
so far i'm not aware of other ways to get AA other then force or app.

have you installed the latest driver, or did you try to do a clean sweep on your current driver?
maybe it will help, but i can't promise it.
i'm on 2x460 myself here, but everything is working just fine :/