To me its also like a downgrade feature.
But well, I use a workaround for this:
Since I need with every wallpaper certain areas for my GeekTool stuff I started to use one .psd file as wallpaper.
http://dl.dropbox.com/u/5905196/Screenshots/screen1.png
So whenever I want to change the wallpaper I just open the psd file and change the one layer.
By doing that the OS wallpaper is always the same: the psd file.
All I have to do after the in-file-change is lock the screen and log in again and all my spaces have the new background.
I guess this should work with every other image file also if you put your wallpapers always on the same spot with the same name and file extension.
Works fine for me.. at least better than changing the wallpaper for 8 spaces or deleting my spacing and setting them up again and assign all the apps to the spaces over and over..