i have the same issue and i notice that this is only happening when the gnome-settings-daemon is running, maybe the problem appeared after the upgrade of gnome 3.4 to gnome 3.6?
i can see that because when im in the lightdm, the brightness control works fine
I really dont know much but this is what happening in my pc, i have a Dell Inspiron N5050 with Windows 7 pre-installed
i have the same issue and i notice that this is only happening when the gnome-settings- daemon is running, maybe the problem appeared after the upgrade of gnome 3.4 to gnome 3.6?
i can see that because when im in the lightdm, the brightness control works fine
I really dont know much but this is what happening in my pc, i have a Dell Inspiron N5050 with Windows 7 pre-installed
sorry if my english is not too good