Comment 2 for bug 867737

The libqapt-runtime package (which handles package installation for Muon including authentication) depends on polkit-kde-1 or policykit-1-gnome, meaning that either package being installed handles the dependency. As long as the polkit-gnome-authentication-agent-1 process is running, the gnome polkit gui will work for this.

It seems, though, that the polkit-gnome-authentication-agent-1 service is restricted to auto-starting in gnome...
The KDE polkit auth agent service also only starts in KDE, too.

At first this would seem to be desirable, as to not have two authentication daemons running at once, but polkit takes care of this. Only one agent can be registered as the authentication agent, so attempting to start the KDE agent after the GNOME agent has started would just cause the KDE agent to quit since it could not register itself with polkit. This means that the OnlyShow=Gnome/KDE entry in the autostart files are unnecessary, and the frontends could be truly interchangeable if this was dropped, fulfilling the current assumptions that the packaging makes.