Comment 46 for bug 762918

Additional info (I am using an Intel GPU, floaters screensaver with custom image) : when the screen hangs, the mouse cursor still reacts. I manage to find the password field, type it, and unlock the screen (the same result can be obtained with gnome-screensaver-command on another tty).

Once I have unlocked the screen, the display doesn't change (still the frozen floaters), but the mouse cursor clearly shows it is now hovering over my desktop (particularly my maximized web browser window). This is why I would also blame the X server.