F28/Xfce - mirror display broken after update

[Robert Moskowitz]

I lost mirror display after this last update and reboot.

In the display panel, the mirror display option is greyed out.  I cannot 
figure out what magic to enable it.

I have set the resolution of the laptop to the same as the monitor; this 
has helped in the past.

The login panel is properly mirrored, but when I log into my account it 
switches to the extended mode where I can drag windows from the laptop 
screen onto the external monitor.

I have tried all sorts of fiddling with advanced options, but nothing 
seems to enable the mirror mode.

:(

Very important here....

thanks in advanced.