Comment 5 for bug 388547

I don't see how this could be a gnome-settings-daemon issue. gnome-settings-daemon has a passive grab on the volume keys, and it will get temporary focus during a keypress so that the keypresses are routed to g-s-d. If a fullscreen game has an active grab on the keyboard or pointer, then there is no way in the X protocol to break this and no way for g-s-d to get the keypresses