NetworkManager has recently added a DNS priority feature that is essential for preventing DNS leaks when using VPNs. It would be nice to see it implemented in the plasma-nm editor. Relevant NetworkManager bug report and patch is here: https://bugzilla.gnome.org/show_bug.cgi?id=758772
As of now this is still unimplemented, and is allowing DNS leaks galore any time the config is edited, and is still a bug in systemsettings (I'm not sure if plasma-nm is the same component, running KDE5) Seeing this fixed is still critical for security.