Screen window displayed each time the brightness change

[Germán Arias]

Hi all, I'm using Trisquel 7 amd64 (ubuntu 14.04) with xfce 4.10.1. Each
time I press a multimedia key to change the brightness, the window
"Screens" is displayed (the window where you change the resolution). If
I press this four times, four windows are displayed (the same window).
This also happens when the laptop become inactive and changes the
brightness, However this don't happen if I change the brightness with
the slider at the panel. There is a way to avoid this? Thanks.