Using the provided xbmc.service, the session/slice is not removed on exit, so on frequent start/stop (by lirc or other), there are a lot of sessions left.

* package version(s)
community/xbmc 12.3-13
core/systemd 212-1
core/dbus 1.8.0-1

Log with problem:
Apr 06 04:21:34 arch xinit[21201]: waiting for X server to shut down (EE) Server terminated successfully (0). Closing log file.
Apr 06 04:21:35 arch systemd[21206]: pam_unix(login:session): session closed for user xbmc
Apr 06 04:21:35 arch dbus[302]: [system] Rejected send message, 2 matched rules; type="method_call", sender=":1.183" (uid=997 pid=21206 comm="(sd-pam ") interface="org.freedesktop.login1.Manager" member="ReleaseSession" error name="(unset)" requested_reply="0" destination="org.freedesktop.login1" (uid=0 pid=301 comm="/usr/lib/systemd/systemd-logind ")
Apr 06 04:21:35 arch systemd[21206]: pam_systemd(login:session): Failed to release session: Access denied

Steps to reproduce:
1) systemctl start xbmc (tested from ssh and remote (lirc))
2) systemctl stop xbmc (see above)
3) loginctl

Workaround (Fix?):
In xbmc.service change add "--exit-with-session" to dbus-launch.

Log whith suggested workaround (Fix?):
Apr 06 04:25:43 arch xinit[21427]: waiting for X server to shut down (EE) Server terminated successfully (0). Closing log file.
Apr 06 04:25:43 arch systemd[21432]: pam_unix(login:session): session closed for user xbmc
Apr 06 04:25:43 arch dbus[302]: [system] Rejected send message, 2 matched rules; type="method_call", sender=":1.197" (uid=997 pid=21432 comm="(sd-pam ") interface="org.freedesktop.login1.Manager" member="ReleaseSession" error name="(unset)" requested_reply="0" destination="org.freedesktop.login1" (uid=0 pid=301 comm="/usr/lib/systemd/systemd-logind ")
Apr 06 04:25:43 arch systemd[21432]: pam_systemd(login:session): Failed to release session: Access denied
Apr 06 04:25:45 arch systemd-logind[301]: Removed session 84.
Apr 06 04:25:45 arch systemd[1]: Stopping User Manager for UID 997...
Apr 06 04:25:45 arch systemd[21428]: Stopping Default.
Apr 06 04:25:45 arch systemd[21428]: Stopped target Default.
Apr 06 04:25:45 arch systemd[21428]: Stopping Basic System.
Apr 06 04:25:45 arch systemd[21428]: Stopped target Basic System.
Apr 06 04:25:45 arch systemd[21428]: Stopping Paths.
Apr 06 04:25:45 arch systemd[21428]: Stopped target Paths.
Apr 06 04:25:45 arch systemd[21428]: Stopping Timers.
Apr 06 04:25:45 arch systemd[21428]: Stopped target Timers.
Apr 06 04:25:45 arch systemd[21428]: Stopping Sockets.
Apr 06 04:25:45 arch systemd[21428]: Stopped target Sockets.
Apr 06 04:25:45 arch systemd[21428]: Starting Shutdown.
Apr 06 04:25:45 arch systemd[21428]: Reached target Shutdown.
Apr 06 04:25:45 arch systemd[21428]: Starting Exit the Session...
Apr 06 04:25:45 arch systemd[21428]: Received SIGRTMIN+24 from PID 21497 (kill).
Apr 06 04:25:45 arch systemd[1]: Stopped User Manager for UID 997.
Apr 06 04:25:45 arch systemd[1]: Stopping user-997.slice.
Apr 06 04:25:45 arch systemd[1]: Removed slice user-997.slice.
Apr 06 04:25:45 arch systemd[21430]: pam_unix(systemd-user:session): session closed for user xbmc