This behaviour comes from the xserver, not gnome-screensaver. It can be disabled by adding Option "DontZap" "true" to /etc/X11/xorg.conf
-- Pressing Ctrl+Alt+Backspace when the screen is locked kills the X session https://launchpad.net/bugs/68695 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
