Comment 12 for bug 1962036

Attaching debdiff which I believe should prevent the service from being stopped on upgrade. Test packages are currently building in ppa:waveform/dbus (https://launchpad.net/~waveform/+archive/ubuntu/dbus) but I've already built locally and verified that the offending portion of the preinst maintscript is gone.

Ultimately this is down to a mis-understanding of debhelper's start/restart options (which are unfortunately named, and in my opinion insufficiently documented -- something I'll try and post a patch for upstream):

In Ubuntu (several releases back) we'd altered the dh_installsystemd options for dbus (in d/rules) to "--no-start" intending the service to be activated solely via dbus.socket. Unfortunately, just specifying "--no-start" tells debhelper you don't want the service started, but it still implies that you wish the service to be *restarted* (if it's running) during upgrade. You must *additionally* specify "--no-stop-on-upgrade" (formerly known as "--no-restart-on-upgrade", and not to be confused with "--no-restart-after-upgrade") if you do not want it restarted.

Debian have also (more recently) adjusted their dh_installsystemd options for dbus (for different reasons), so this will also need patching upstream (I'll try and open a bug for this and associate it with this one as it's all the same options affected at the end of the day).