I installed both sharing /home. Prior to the (second) incident of the problem
I had just aborted (midway) restoring the backup of my earlier setup.
Before installing Trisquel I did a backup of /home and wiped the hdd. After
installing I wanted to restore the backup, but midway I figured that I might
run into trouble, espacially with folders of certain applications. I realised
that I should only restore/copy the content of the basic folders such as
Documents, Downloads etc.
Anyway, the reason to reinstall Mint was, that I wanted to starts from
scratch, Trisquel being my main OS.