My hypothesis is that the Optimus technology in the Acer's NVidia had caused this - what do you think, Inland and Jenny? Did the Optimus cause the swith to low end graphics upon running the screenshot taker with the game?
Yes, Optimus has been known to do that with games where it doesn't correctly sense that the game needs better than low end graphics. I suspect Optimus might be more prone to have this problem with 2.5D games (3D characters on a 2D background) than with fully 3D games, but running the screenshot program alongside the game may have also caused a problem.