Comment 28 for bug 388547

Sorry, I don't think you're going to love this answer, but there's not a lot X can do about it.

As mentioned in the Ubuntu bug, some games decide to grab the entire keyboard when running full-screen. This is specified to override everything else and give that client sole, exclusive, use of the keyboard. I'm not sure why they do it, but I'm guessing it's so they can be sure Alt-Tab doesn't accidentally trigger or something, which would be deliberately disabling hotkeys.

Anyway, if the game developers tell us there are shortcomings in our input model that we need to fix so they can stop grabbing, we'll be happy to take a look. But for the moment, we're just doing what we're told, which is: grab the keyboard to the absolute exclusion of everyone else.