To be more exact: service that dos not start anymore after I enable and later disable it is avahi-daemon.service. It is told in that unit file that: Alias=dbus-org.freedesktop.Avahi.service.
In fact, it seems that any operations using dbus (NTP, avahi...) have problems after starting openvpn service and it does not vanish if I stop it. So, it seems that either openvpn sevice (or possibly NM) creates policy some policy kit rule that does not vanish when I disable and stop openvpn.
