When you try to customize the button layout (xfwm4-settings) you get a corrupted layout that you can't repair. Well you can but it's tricky.
I can reproduce this with latest git master.
I found out two things:
1. From GTK+ 2.20 on we have to use gtk_buildable_get_name() instead of
gtk_widget_get_name() to obtain the ID of the buttons in the glade file.
This can be fixed easily.
2. Dragging layout buttons results in a number of warnings. Something seems
to be broken here as well.
Ok, the drag source and target IDs were also obtained using gtk_widget_get_name() which is wrong. Fixed in master:
Author: Jannis Pohlmann <firstname.lastname@example.org>
Date: Sun Nov 14 12:56:27 2010 +0100
Fix broken button layouts by obtaining button IDs correctly (bug 6824).
Since GTK+ 2.20, gtk_buildable_get_name() needs to be used instead of
gtk_widget_get_name() (which always returns 'GtkButton' in this case).
*** Bug 6828 has been marked as a duplicate of this bug. ***
*** Bug 6797 has been marked as a duplicate of this bug. ***
*** Bug 6878 has been marked as a duplicate of this bug. ***