Desktop Wallpaper folders disappearing in System Prefs

Whenever i try to add a picture folder to the system preferences to manage my wallpapers, the instant i close the system prefs window, all the folders i added disappears...

I'm on mountain lion on a brand new install from 2 days ago. I never had this problem on Lion or Mountain Lion (before i made a clean install)...

I found 3 other post from people with the same issue, do you know what the problem might be and what to do to fix this? It's really annoying!

Here are the 3 others posts about this:

https://discussions.apple.com/thread/4105775?start=0&tstart=0

https://discussions.apple.com/thread/4179362

http://forums.macrumors.com/showthread.php?p=15556826#post15556826

Thanks for your help!