Cinema Display + PB + Desktop backround image


I have a real quirky problem that has been bugging the c**p out of me. I have a 15" powerbook and a 20" cinema display. The way I normally use my pb is that I use my cinema display with my pb screen closed. The problem that I have is that everytime I disconnect my pb from my cinema display or visa versa my screen background picture is lost and all I get is a blue background screen. This is quite annoying since I disconnect and reconnect my pb from my cinema display on a daily basis. And if I want a background image I have to reset it every time.

Any ideas on how to solve this problem? Oh I'm running Mac OS 10.3.9.
I am dual screening my PB 12" with a 17" CRT monitor and when i disconnect the display i have similar problems. In the past i have sent the machine to sleep before disconnecting the display, hopefully when you wake it up it will format correctly?
Nope, this doesn't help. This is my normal mode of operation. I always put my computer to sleep before I unplug the display. The only thing that seems to work is if I shut my computer down every time I disconnect my external display. But, when I put it to sleep the background image gets messed up.