Multiple desktop problems SOLVED, mostly

[rikona]

I had quite a few problems after installing kubuntu-desktop to 16.04
Ubuntu, as you may have seen in multiple threads here.

The best solution I found was to reinstall Ubuntu into a FORMATTED /
disk, leaving /home, on another disk, as-is. Trying to install Ubuntu
without formatting / did not work that well - it apparently kept too
much stuff in /. Most of the many problems I saw are no longer there.
A small number remain, and these may be due to things in /home, so I
still have a bit of cleanup to do. 

Overall, I would strongly recommend AGAINST installing kubuntu-desktop
to 16.04 Ubuntu. The KDE part did not work well AND it seriously
messed up the Ubuntu desktop as well.

I am back to where I started, with several KDE pgms individually
installed in Ubuntu. This approach works much better than trying to
have both desktops. Not perfect, but reasonably good with relatively
minor problems [copy/paste between them sometimes does not work, for
example].

I would like to give MANY thanks to the folks who helped me with this,
especially Nils and Colin.

-- 
Best regards,
 rikona