Hey!
Sorry for not including this info in my first post - I feel kinda nooby now... 
ObjectDock Plus 2 v1.97
DeskScapes 3 v3.20
Windows 7 64-Bit
Catalyst™ Version 10.6
2D Driver Version 8.01.01.1038
Direct3D Version 8.14.10.0761
OpenGL Version 6.14.10.9901
The problem seems to be caused by the combination of DeskScapes and ObjectDock. Using a regular wallpaper or a solid color as a background doesn't cause this phenomena.