Comment 8 for bug 1773859

# dpkg -L systemd-shim
/.
/usr
/usr/lib
/usr/lib/i386-linux-gnu
/usr/lib/i386-linux-gnu/systemd-shim
/usr/lib/i386-linux-gnu/systemd-shim-cgroup-release-agent
/usr/lib/systemd
/usr/lib/systemd/ntp-units.d
/usr/lib/systemd/ntp-units.d/systemd-shim.list
/usr/share
/usr/share/dbus-1
/usr/share/dbus-1/system-services
/usr/share/dbus-1/system-services/org.freedesktop.systemd1.service
package diverts others to: /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd
/usr/share/doc
/usr/share/doc/systemd-shim
/usr/share/doc/systemd-shim/copyright
/usr/share/doc/systemd-shim/changelog.Debian.gz

# cat /var/lib/dpkg/info/systemd-shim.postrm
#!/bin/sh

set -e

if [ "$1" = remove -o "$1" = purge ]; then
        dpkg-divert --package systemd-shim --remove --rename --divert \
                /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd \
                /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service
fi

# Automatically added by dh_installdeb
dpkg-maintscript-helper rm_conffile /etc/dbus-1/system.d/org.freedesktop.systemd-shim.conf 8-4 systemd-shim -- "$@"
# End automatically added section
# Automatically added by dh_installdeb
dpkg-maintscript-helper rm_conffile /etc/dbus-1/system.d/org.freedesktop.systemd1.conf 6-2 systemd-shim -- "$@"
# End automatically added section

The error was:

Removing systemd-shim (9-1bzr4ubuntu1) ...
Removing 'diversion of /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service to /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd by systemd-shim'
dpkg-divert: error: rename involves overwriting '/usr/share/dbus-1/system-services/org.freedesktop.systemd1.service' with
  different file '/usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd', not allowed

I have no idea what the dpkg-divert error means there, but I assume there's some interaction I'm not following with the divert...