Where I am at ...
It seems to me that there may be a conflict between governor control using "cpupower" and having the panel App "mate-cpufreq-selector" running (if only for visibility). 
The panel app does not look to adopt settings that are currently active but, instead, enforce a programmed default at startup. My opinion is that using that approach is incorrect.
Next, once the App is running, if I use cpupower to set values, the App will show those values but, after some random delay, it takes over and imposes an "ondemand" governor.
I have removed the panel App, and it seems that nothing is "interfering" with my manually set governor. So I will have to live without the visual of the status on the panel App's display! "Woe is me!!!"
So .. that is the end of that conflict. I will eventually submit my "findings" to those responsible for the panel App.
I am shifting my attention to addressing the next phase in this journey: creating a startup service for systemd! 