Comment 36 for bug 310270

This is not an X11 bug. It is a hardware flaw in the Dell M1330's touch-sensitive multimedia buttons. Regardless of how long you press the buttons, they always generate a keypress event with a duration of about 680 milliseconds. This is long enough to trigger the typematic repeat with the default settings. You can work around this problem by setting the typematic delay to 700 milliseconds or longer, but that is a workaround, not a solution.

I know that GNOME handles these keys correctly, so it would probably be worthwhile to ask the person in charge of GNOME's media key support how they do things.