This is a problem I've only had with KDE recently. I am using the version of KDE that is being shipped with Kubuntu, and I'm using it on a laptop. While running KDE I am receiving arbitrary display change notifications (and I am not even changing any display settings). They come in the form of a large white box in the centre of the screen, and they will say on of two things: Display Change: LCD Off, Brightness: 0%
Once again: this only happens on KDE, not Gnome or any other desktop manager I've installed.