Two power icons in Xubuntu

In Xubuntu 16.04.3 (and several previous versions aswell) it is not possible to have no power icon in the notification area.

A power icon is displayed even though 'Show system tray icon' is unchecked in Xfce Power Manager.

When 'Show system tray icon' is checked, there are two power icons displayed.

(See screenshots)

I've searched and I can't find any information related to this in Xubuntu/Xfce.

Is there a way to fix or work around this bug?

A right-click on the panel (taskbar) opens a menu. Choose Panel > Panel Preferences... and the panel preferences window will open. In this window choose the Items-tab, look for the Power Manger Plugin and remove it with a click on the --button.