@Sebastien: actually, I don't know how to run gnome without a panel. :) It's probably not a gnome-panel bug, it's a problem with changing screen brightness. So that means it's an xorg bug?
@Geir: I tried a little more and I can now confirm that a random flash (with me doing nothing on keyboard mouse etc.) does not change the file /var/log/Xorg.0.log. As I said in the updated description, my current conjecture would be that it is related to brightness changes of the screen.
@Sebastien: actually, I don't know how to run gnome without a panel. :) It's probably not a gnome-panel bug, it's a problem with changing screen brightness. So that means it's an xorg bug?
@Geir: I tried a little more and I can now confirm that a random flash (with me doing nothing on keyboard mouse etc.) does not change the file /var/log/ Xorg.0. log. As I said in the updated description, my current conjecture would be that it is related to brightness changes of the screen.