It sounds as if both gnome-screensaver (or xscreensaver) and workrave are fighting for access to mouse movements,.
** Bug 42769 has been marked a duplicate of this bug -- workrave hangs after unlocking with input blocked https://launchpad.net/bugs/20070 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
