I can confirm this defect and add the following information.
Without using the proprietary driver (ATI/AMD FGLRX), the brightness UP and brightness DOWN pop up the brightness window but DO NOT alter the brightness. I can alter the brightness via the gnome applet
If I use the propietary driver then the buttons do not work and I cannot alter brightness via the gnome applet.
I can confirm this defect and add the following information.
Without using the proprietary driver (ATI/AMD FGLRX), the brightness UP and brightness DOWN pop up the brightness window but DO NOT alter the brightness. I can alter the brightness via the gnome applet
If I use the propietary driver then the buttons do not work and I cannot alter brightness via the gnome applet.