xfce4 xfdesktop time to time crashes without visible reasons.
On system startup all is ok but after a while wallpaper and right click menu disappears.
When I manually start xfdesktop (Alt+F2) it works fine some time but then disappears again.
It helps if you mention which version of opensuse you are running.
Is what you are describing similar to what is reported in (http://forums.opensuse.org/english/get-technical-help-here/applications/458983-i-tried-xfce-now-i-am-back-kde.html)
openSuse 11.4
XFCE 4.8.0