When I'm at my desk I use an external display and desktop spanning. However, also benefiting from mobility I also take my PB out once in a while. I disconnect all cables then close my PB. However, when I come back I open my pb and hook everything up. When my external monitor "kicks" in, I's just the generic blue background. Everytime I have to open the system prefs and click on and off the "Change display every minute" setting to remind the computer of it's wallpaper. Any idears?