Calling GraphicsDevice.setFullScreenWindow(null) should restore the currently active FS window to the normal mode. That is, the size of the frame should be equivalent to what the user has specified. But when calling this on linux + xinerama (virtual screen having 2 monitors), the fullscreen frame is not restored to normal size and still continues to occupy the full screen. On Win32, Solaris9, this works fine. On linux without multi-mon setup, this works fine. This is reproducible on all releases since 1.4 on linux+xinerama (multimon). I tested this with Linux RH 9.

I have attached a sample test. Run it on the above config. You will see a fullscreen frame being displayed on the primary screen. Click on the button in the frame. If the frame does not get restored to normal size (200, 200), the bug is reproduced.