I've had the same problem for over a month now, where my wallpaper will revert back to an old one when restarting the computer. It's frustrating because I have a wallpaper of me and my gf at home, but change it when I have to go for presentations. 75% of the time when I turn it back on it will have reverted to the picture of me and her or another old one. Also when I right click on the Desktop and "Change Desktop Wallpaper" the menu will not pop up. I have to go and manually click on the button, or go through Sys Pref. Moreover, the folders I add for wallpapers will NEVER save, I have to continuously add them every time I open the menu. I've haven't read of hardly anyone having the same issues (and it's strage that they're all Wallpaper-related), which is why I'm hesitant that it would be address in 10.8.2. I've tried a terminal command recommended in one of the few threads I found (https://discussions.apple.com/thread/4144290?start=0&tstart=0), but it hasn't worked.