Don't throw your AMD cards away just yet folks, because I'm having the same problem, and am running Nvidia prop. drivers. Other users have clearly stated that they are having similar problems with Intel HD. So it only makes sense to graduate from the AMD video driver theory. I am inclined to think that it has something to do with Compiz, but if not everybody having this issue is running Compiz, then out the window goes that theory. But I am thinking Compiz, because I have 3 Print Screen images on my desktop as we speak that were taken before I got Compiz up and running. And the Print Screen function worked flawlessly, or at least it worked as expected. Is there a connection? I can't say for sure, because I just discovered the issue, but in my mind, it's more probable than specifically AMD drivers. It's probably good to include that I am running LM13-Mate right now and love it--all except for the "broken" Compiz behavior. This is a huge step for me, because I am finally breaking away from LM9.
By the way, there are a few really good posts that help get Compiz running, but it is still nowhere near what it was in LM9. There was also an update the other day that seams to have made Compiz go a little wonky. The bottom line is Compiz ain't what it used to be. No matter what tweaks you make to the window manager settings in mateconf-editor, or the gtconf-editor for that matter, Compiz really creates problems for other 3D processes like rss-glx screensavers, and I'm sure other things. System Monitor might show CPU efficiency nice and low, but try running a 3D screensaver, and it will skyrocket. Not to mention that the screensaver rendereing itself absolutely sucks.
I'm sure Clem knows about this, and things have fallen way behind in the 3D world. Hope things can get back on track like they were in LM9. That's my only gripe right now. I still love Mate, it has come leaps and bounds since it's inception, but alas, we have leaps and bounds more to go. However, huge thanks be to Clem and all his hard work.