“Question: I note at the bottom of the root display, there is a red bar saying ‘configured as extender’. What did I do to cause this message? What does it mean?”
That message means the controller has been configured as ‘remote extender’ mode. This happens when you set a zone on the master controller to point to a remote controller — the UI will automatically configure the remote controller in ‘remote extender’ mode. If you want to remove that mode, just click on that bar and it will prompt you to disable extender mode.