Comment # 9 on bug 1020363 from Simon Lees

(In reply to Marius Kittler from comment #0)
> ## Observation
> 
> 
> It seems that pulseaudio and `spice-vdagent` are preventing the old session
> to close. When starting also pulseaudio via systemd and killing
> `spice-vdagent` before isolating the graphical target the issue doesn't
> occur.
> 
> I think starting D-Bus via systemd is the right thing to as it allows usage
> of `busctl` for instance. It should be possible to reduce the problem by
> also starting pulseaudio via systemd. Not sure about `spice-vdagent`, though.
> 

Another controversial fix could be to build systemd without the
"--without-kill-user-processes" flag which seemed to be the systemd upstream
way of dealing with this issue.