Struts are not properly updated on a non-primary device

Since at least Xfwm4 4.16.0.

In a multi-monitor configuration, with a panel on a non-primary monitor (without autohide or "Don't reserve space on borders"), moving the panel does not update the struts. However, if the active window is remaximized, the struts are updated.

The property change is sent to the window manager by the panel independently of the monitor status. This works with Openbox.