In gtk-xfce-engine/gtk-2.0/xfce_theme_draw.c in function draw_shadow widget may be NULL (note the condition "if (widget && GTK_IS_SPIN_BUTTON (widget))"), but gtk_widget_get_parent is called without checking for it.

This leads to printing warning

Gtk-CRITICAL **: IA__gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

in some programs --- at least in pgadmin3, when dragging panels.