As Wutpa stated--using print screen when playing in fullscreen mode-all i get is a snapshot of my desktop,not the game screen.
Had the same problem. The solution is to disable aero and then take the screenshot. (the problem is caused only in fullscreen mode and NOT on windowed)
Unfortunately, from what i know, you can't disable aero on win8.
So, the only solution is to proceed with a recording for few seconds and then extract the frame or take a screenshot while you playback the file with your player.
Luckily for me on the ''glorious'' win7, you can disable or enable aero at will.