Icons on Xfce Desktop come back

I am running Hiweed 2 RC3 (a Linux distribution based on Ubuntu), which uses Xfce as its desktop environment.

One month ago, for some unknown reason, all of the icons on my desktop disappeared after I restarted my computer. Today I was free to play with my computer and got the icons back as follows:

• Go to Menu>Settings>Xfce Setting Center>Desktop
• Click "Allow Xfce to manage the desktop".

Great! All icons came back, BUT, what on earth un-checked this?