1- Something grabs mouse: ie: virtual machine window, or GTK menu in an application or an indicator
2- Screensaver attempts to start, but cannot get exclusive lock on mouse
3- DPMS turns monitor black
4- User moves mouse, which turns the screen back on
5- Mouse movement causes mouse to get ungrabbed by vm window or gtk menu
6- Screensaver can now grab mouse, and starts
This is all related to the fact that X does not have an API that will let the screensaver tell an application to release mouse and keyboard grabs.
This is likely what happens:
1- Something grabs mouse: ie: virtual machine window, or GTK menu in an application or an indicator
2- Screensaver attempts to start, but cannot get exclusive lock on mouse
3- DPMS turns monitor black
4- User moves mouse, which turns the screen back on
5- Mouse movement causes mouse to get ungrabbed by vm window or gtk menu
6- Screensaver can now grab mouse, and starts
This is all related to the fact that X does not have an API that will let the screensaver tell an application to release mouse and keyboard grabs.