I can confirm what you found out. Great work! 
The only solution I see for now is to suppress these messages in the logfile. I found similar issue with sogo here and in the docs and changed it to fit to our needs:
echo "if \$programname == \"dbus\" and (\$msg contains \"Activating via systemd: service name='org.freedesktop.timedate1'\" or \$msg contains \"Successfully activated service 'org.freedesktop.timedate1'\") then stop" > /etc/rsyslog.d/ignore-dbus-timedate.conf
systemctl restart rsyslog
@giacomo, do you see another way to get rid of these messages triggered by the subscription module?