This is a problem on Dell Inspiron 6400 as well. I've installed 915resolution to fix the resolution so I suspect this might be the culprit but I didn't test the keys before, unfortunately.
Regards Andreas -- Dell Inspiron 640m/E1405: changing brightness by hotkey doesn't work anymore https://launchpad.net/bugs/70758 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
