Question: Problem saving procedures in Linux Mint

Hi,
I have aproblem saving procedures. I am using Linux Mint 18.2, KDE, 64 Bit. Everything works (at least what I used until now) except:
when trying to use save "save(kgVnat,"kgVnatproc.m") I get an error message "Error, permission denied: no write access (kgVnatproc.m)". Now - the work direcxtory is "/home/username" - in the status bar as well as per currentdir() or currentdir(kernelopts(homedir)) . I can create and save files there - and also in the working directory of maple "/home/username/Studium/Maple" by using a file manager or a text editor - everything else would anyway be surprising when using home/username directory. So it has to be something else ...
I can save the worksheet as a whole without any problems in "/home/username/Studium/Maple". Also I tried to use currentdir(..) to change to the directory explicitely and then saving the proecdure, but again, "..access denied" even though worksheets are saved without error...

Anyone any idea?

Kind regards Udo