I found an odd behavior:
Start live tv on a Client (OpenCable tuner on Server), without pressing stop on live tv, navigate to Video and play some files => The tuner is not released (Server says "serving client").
Stopping playback of video files on the Client has no affect (Server tuner not released).
Closing MC on the Client has no affect (Server tuner not released).
Rebooting the Client machine has no affect (Server tuner not released).
Re-open MC on the Client has no affect (Server tuner not released).
If I hard reboot the tuner, the Server complains about "no data received in 30 seconds" and still says "serving client" (but the LED on the tuner is actually no longer busy). Only way out is to restart MC on the Server.