Comment 6 for bug 804435

I confirm this bug, and it really seems to be caused by nautilus. In fact, if you disable nautilus autostart (by removing the /etc/xdg/autostart/nautilus.desktop file), the desktop background will not be painted.

Then, if you start "nautilus -n" manually from a terminal, you'll see the desktop background being shifted a few pixels to the right, and then reverting back to the correct position. This happens also when metacity is not running, which seem to exclude a window manager bug.