It might be that those keystrokes (AltGR) are "dead" in your currently configured keyboard. I'm fairly new to Linux so I'm not able to help you here; all I know is keyboards get configured via HAL now and the HAL database is not as complete as we would all wish it to be. I suspect some keyboards get detected imperfectly, as do some touchpads (and probably mice too). Of course, I may be on the totally wrong track here...