First of all: I'm beginning to hate all non-anonymous SourceForge services.
But going back to the topic: right now I've got very little lxde components installed,
more or less lxsession and lxpanel with their deps. I also don't have any desktop wallpaper set,
so the background (after 'xseroot -grey') *should* be solid gray.
However, often I see there small rectangles with parts of other windows (some of them from different desktops).
Back on the console, I see a few BadMatch/Window/Pixmap/Drawable errors.
I suspect the reason lies in the non-trivial effects of gtk client-side windows (http://library.gnome.org/devel/gtk/stable/gtk-migrating-ClientSideWindows.html).
While the code seems to use that GDK_WINDOW_XWINDOW macro, it seems it doesn't help in every case.