When I try to remove those two packages, apt-get wants to also remove kubuntu-desktop-trinity AND it says that since *those* guys are gone, autoremove will remove all *these* packages, too, and proceeds to list about 75 other packages.
I have no idea why this happens. Perhaps package dependancies in Kubuntu repo are screwed up? I also don't know any reasonable way to prevent deinstalation of other 75 packages. I think you might be able to pin them but that would be tedious and I think it would prevent you from getting updaes to those packages (not sure).
Janek