I've followed all the solutions proposed to make the desktop wallpaper change, as it apparently it doesn't, but the only solution I can achieve is getting the default wallpaper after rebooting.
However my issue is slightly different than the one other users have reported.
When I change the desktop, I can see in the system preferences that it has changed, and even when using mission control, or switching from a space to another, I see the new wallpaper, until I go back to the desktop (either the current one or the new one).
So it seem that the wallpaper actually changed, but is "overlapped" by the default one, as it's using multiple layers.
I'm not sure if I've made the issue clear.
I don't have any application playing with the wallpaper (I use to have Kuvva (www.kuvva.com) installed, but then I've removed using a specific uninstaller).
Oh, and my system is a Mac OS X Mountain Lion.
Anyone has a possible solution?
UPDATE When changing the wallpaper, the system log doesn't show anything in particular, except, sometime these two lines (but this is not a constant):
Sep 6 13:05:36 new-host.station System Preferences: *** WARNING: -[NSImage compositeToPoint:operation:] is deprecated in MacOSX 10.8 and later. Please use -[NSImage drawAtPoint:fromRect:operation:fraction:] instead. Sep 6 13:05:36 new-host.station System Preferences: *** WARNING: -[NSImage compositeToPoint:fromRect:operation:] is deprecated in MacOSX 10.8 and later. Please use -[NSImage drawAtPoint:fromRect:operation:fraction:] instead. S
The uninstaller I've used has been provided by the Kuvva support team: this is the only feedback I got from them. Further question never got answered. And no, I didn't install it from the App Store.