Comment 2 for bug 959825

This appears to also happen even if you are actually running 3d, but another user is running Unity 2d.

I had this problem. I was logged in specifically to the "Unity" desktop, and had the compiz cube, so I know it was 3d. But my sister was also logged in with Unity 2d on her user. MyUnity had the normal 2d restrictions. Then I opened a terminal as root and using top ended the gnome-session process for my sisters user (which basically logs them out). Then MyUnity did fine.