This has been reported in launchpad
https://bugs.edge.launchpad.net/ubuntu/+source/coherence/+bug/621722
VLC: sees it perfectly - if the server is active when VLC starts, VLC displays it. If it deactivates while VLC is running VLC delists it, if it restarts while VLC is running, VLC lists it again. All media is browsable and playable - perfect behavior.
Coherence uPNP inspector: If the media server is up when the inspector starts, the inspector lists it. If it deactivates while the inspector is running, the inspector delists it. BUT if the media server is then brought back UP, the inspector DOES NOT RE-LIST IT (even when "rediscover devices" in the file menu is selected). However if the media server is down when the inspector is started and then is started, the inspector DOES add it correctly. When the server is seen by the inspector, the inspector can correctly browse its contents.
Rhythmbox just plain never sees the media server at all (and I checked in the device addition signal handler - it never receives notification that a device is there under any circumstances), although it CAN see a mediatomb server on another PC in the home network.
I conclude that there is a small bug in coherence itself, or the inspector - whereby a server that deactivates and then reactivates is not being successfully re-added. And there is a more significant bug in the Rhythmbox plugin whereby it is never being notified of the existence of a server on 192.168.1.1. Of course Rhythmbox has its own issues concerning the listing of tracks from UPNP media servers such as mediatomb - but that is dealt with in another bug report.
