Disappearing wallpaper
I have a 21" iMac running Lion OS.
Just recently, I am not able to get wallpaper to stick to my desktop. Whenever I select wallpaper it stays around for the session, but when I leave and return the wallpaper appears for a moment and then is replaced by a solid blue background. (The toolbar and 4-5 files I have saved to the desktop remain.) It's like my iMac has a mind of it's own.
Any tips on how I can fix this minor but frustrating issue would be much appreciated.
Thanks!
iMac, iOS 6.1.4