gtkpbbuttonsd-gnome 0.6.8-2 brightness pop-up

[Giovanni Ridolfi <gio.rido@tiscali.it>]

Hello everybody,
I've a ibook G4 (PowerBook6,5)

I'm running sid, Gnome 2.12 + linux-image-2.6.15-2
+ gtkpbbuttonsd-gnome 0.6.8-2

When i press Fn+[F1,F2] I  
both cannot change the brightness level of my LCD 
and the small popup window does not appear
(whereas I can change the speaker volume and also when I eject a
CD the pop up windows appear).

Any hints?
-) RTFM
-) install gtkpbbuttonsd
-) fill a bug report
-) do some debugging.... how?
 
TIA

Giovanni