Comment 20 for bug 263211

An obvious patch appears to be:

--- src/gs-manager.c.orig 2008-10-10 18:28:13.000000000 +0100
+++ src/gs-manager.c 2008-10-10 18:28:21.000000000 +0100
@@ -1281,9 +1281,9 @@
         pixmap = gnome_bg_create_pixmap (manager->priv->bg,
                                          gs_window_get_gdk_window (window),
                                          width,
                                          height,
- TRUE);
+ FALSE);
         gs_window_set_background_pixmap (window, pixmap);
         g_object_unref (pixmap);
 }

This will make gnome_bg_create_pixmap just call gdk_pixmap_new() passing in the window, width and height; instead of calling make_root_pixmap() which makes an X root pixmap.