If compiz is used and "Unredirected Fullscreen mode" is turned on the gnome-screensaver keybord grab does not work. Its possible to input into (hidden) windows then. 

My current understanding is that when compiz finds a fullscreen window, it calls "XCompositeUnredirectWindow()" on it. This seems to have a side effect that breaks the keybord lock for some reason without gnome-screensavers noticing (no GdkEventGrabBroken is sent). So it assume it has the keyboard grab already, when in fact it does not have it (anymore):

[gs_grab_move_keyboard] gs-grab-x11.c:324 (00:41:01): Window 2200024 is already grabbed, skipping
[gs_grab_move_mouse] gs-grab-x11.c:264 (00:41:01): Window 2200024 is already grabbed, skipping

my proposed fix changes the code so that it will always (re)grab the keyboard when the unlock dialog comes up.

diff -u ref/gnome-screensaver-2.20.0/src/gs-manager.c gnome-screensaver-2.20.0/src/gs-manager.c
--- ref/gnome-screensaver-2.20.0/src/gs-manager.c	2007-10-17 21:42:29.000000000 +0200
+++ gnome-screensaver-2.20.0/src/gs-manager.c	2007-10-17 21:25:29.000000000 +0200
@@ -1050,7 +1050,7 @@
         }
 
         /* Move keyboard and mouse grabs so dialog can be used */
-        gs_grab_move_to_window (manager->priv->grab,
+        gs_grab_grab_window (manager->priv->grab,
                                 gs_window_get_gdk_window (window),
                                 gs_window_get_screen (window),
                                 FALSE);




This is reported on ubuntu as https://bugs.edge.launchpad.net/ubuntu/+source/gnome-screensaver/+bug/145123

Please let me know what you think about this. I'm happy to provide more logs if required.

Thanks,
 Michael