I just debugged the problem a bit and it only happens if no
"kubuntu-desktop" package is installed. So as a workaround I would suggest to run:
$ sudo apt-get remove kubuntu-kde4-desktop; sudo apt-get install kubuntu-desktop
and to retry the upgrade then.
I just debugged the problem a bit and it only happens if no kde4-desktop; sudo apt-get install kubuntu-desktop
"kubuntu-desktop" package is installed. So as a workaround I would suggest to run:
$ sudo apt-get remove kubuntu-
and to retry the upgrade then.
I look into the problem now for a better fix.