Sorry, actually fade-out to xscreensaver can be interrupted by pressing a key, but not by mouse movement. You can replicate the problem if you set up "fadeSeconds" to bigger value, e.g. 30 seconds and then activate the screensaver. Pressing a key stops the fade-out process and mouse movement doesn't.
- Bug#706791: xscreensaver: Fade-out to xscreensaver cannot b... robot.r2d2
- Bug#706791: xscreensaver: Fade-out to xscreensaver can... robot.r2d2
- Bug#706791: xscreensaver: Fade-out to xscreensaver... Jamie Zawinski