my problem is the following:
after the installation of Linux Mint 13 XFCE I had the mint menu, but not the wallpaper I expected. It was the standard XFCE one: blue, with mouse in the centre, not the official Mint one. I then right-clicked on the desktop, chose "desktop settings" and then clicked on the "+" symbol to add my own wallpaper / background. That worked fine, but after reboot the background was the standard XFCE one (with mouse). If I right-click on the desktop, it changes to the official Mint theme one, but to have my photo back as a wallpaper, I have to select it again from the list.
I have no idea how to make the custom background stick. Any ideas?