Prioritized labels
Drag to reorder prioritized labels and change their relative priority.
Other labels
This issue shows in thunar because of an issue in an underlying library (Gtk / GLib / Gio / Gvfs /...)
A link to the underlying issue should be added to the thunar issue. It might sense to keep to thunar issue open in order to implement a workaround.
5. Window Properties / Messages
Xfce / xfwm4
Attributes set at the window level defined by FreeDesktop.
Prioritized