I found the solution for this bug. KDE needs the package "polkit-kde-1" to popup the authorization dialog for system updates or network shares. It seems that the package does not install when installing the "kubuntu-desktop" meta package. Looks like a dependency problem in the packages.
Nevertheless, if you want to get rid of this bug, just install "polkit-kde-1" and all problems are gone.
I found the solution for this bug. KDE needs the package "polkit-kde-1" to popup the authorization dialog for system updates or network shares. It seems that the package does not install when installing the "kubuntu-desktop" meta package. Looks like a dependency problem in the packages.
Nevertheless, if you want to get rid of this bug, just install "polkit-kde-1" and all problems are gone.