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: commit a3225e2e116a68833994349c949cd6fb0b6fdaae Author: Jannis Pohlmann <jannis@xfce.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. ***