On the mac I used the RDP client from the app store.
The configuration enables to start the connection and authenticates up to a full black screen then it breaks the connection and returns to the PC widget.
On the MATE-System a logged-in user with the same name gets a logout.
Where could I get some error log to dig into the problem causes?
Instructions I've seen on installing and connecting to Ubuntu specify creating the ~/.xession file and entering
mate-session
into it. The two 'unset' statements prior to that call resolved the problem for me. You've got me now searching to find where I found the solution. Everything I see right now simply says to put the 'mate-session' into the ./.xsession file.