Here’s another possible clue to what is happening: When the STB is tuned to the channel the and the source stream restarts the STB will continue to play the video. If the STB is tuned away from the channel and back again it will only see the audio, as would a new subscriber (STB, VLC, etc). It seems that the MPEG-TS PMT loses the video stream from stream 0, however the STB has already registered the PMT from the previous (complete) stream. As such it knows to look for stream 0. New subscribers are only informed of stream 1 (audio) and therefore don’t attempt to tune the video.
Granted this is a theory..I can provide a tcpdump if you are interested…