Comment 3 for bug 1596751

Your opinion disagres with the xfce4-settings documentation:

http://docs.xfce.org/xfce/xfce4-settings/display

See section "Primary display":

"Check this option to provide a hint to panels, docks and the desktop that the selected display is the primary display."

If you want panels on every monitor you could choose not to have a primary display selected.

Your proposed behavior anyway is not user friendly. After configuring your primary monitor in xfce4-settings you have to enter the panel settings again and configure the monitor where you want the panel. If this is true for each software (panel, docks, icons) you have a lot of configuration to do when you plug in a larger monitor (but only on your right, if the monitor is on the left you're a lucky guy).

I guess this is linked to a long running xfce bug that never made it to xfce4-panel.

https://bugzilla.xfce.org/show_bug.cgi?id=8328