Not possible to change desktop wallpaper

I run several desktops on my macbook pro and i now want to change the desktop wallpaper. This works fine on desktop 2,3,4 etc but not on no 1 (the default one). On every restart it goes back to the "space/galaxy" background.

Even if i use own pictures, colours or the wallpapers that comes with the mac.

It seems like a bug to me. How do I solve this?