I'm experiencing a bug that's very likely related to this one. On my HP DM1z, when I press the brightness shortcut keys on my keyboard, two display choice windows open. Pressing the brightness keys multiple times to quickly change the brightness can quickly result in dozens of windows open. Using XFCE 4.10.
I forgot to add that I expenrience this bug only when using proprietary fglrx graphics driver. If I switch to OS radeon driver, keys change brightness as expected without display choice windows popping up.
I fixed this problem by going to Main Menu -> Settings Manager -> Keyboard
-> Application Shortcuts and removing the XF86Display mapping.
I think the ATI driver does something to make the brightness keys send that
key for some reason.
So you think the problem is definitely with the ATI driver? By the way, I did a brief stretch on Mageia 4 Cauldron about a month ago, and this bug started to manifest itself in Gnome as well. So maybe it's not an XFCE problem after all. I wish AMD had and easier way to report bugs to them cause that's seem to be where the problem is.