Just a quick follow-up to let you know about those issues:
I changed the DVICO USB tuner for a Cinergy 2400 PCI-E tuner (double DVB-T tuner, a really great card). I reinstalled GBPVR and I do have the same exact issue :
* GBPVR "stops" on program boundaries
* GBPVR "lock" the tuner to a frequency
I don't need that you diagnose this problem, I'm now using SageTV and with SageTV (as well as with MediaPortal / MyTheater / WebScheduler), I never had a "tuner lock".
So there is maybe something special on my PC that GBPVR doesn't like (it is an Intel Dual Core), but it seems to me that GBPVR is good at revealing this problem , right now I'm thinking of a sort of "race" condition : GBPVR think it has released the tuner but in fact it is not or something like that (In fact the "locking" does occur when the recording service crash when it shock on program boundaries with Mpeg mux or DVR-MS mux).