Comment 29 for bug 527157

James: no, there is no need to touch kernel. You should have noticed, that brightness control works as expected, before you login (during boot or even on login screen).

Problem is in user-level process running during user session. We have to find that process, than fix will be pretty simple.

See plugins/media-keys/gsd-media-keys-manager.c:1528, function do_screen_brightness_action_real(): looks like it is correct place for patch.
Later I will think on good solution.