If it happens again, have a look in your GBPVRRecordingService.exe.log to see if there were any errors listed between the expected start and end times for that show.
It seems unlikely it had anything to do with being in the menus and such, since the recordings are done via the recording service and thus independent of the client application.
When I had this trouble it was only when recording from the composite input. Recordings from the coax worked fine so it took me a while to figure out what was making it happen. Could this be the case for you too?
I also have this problem. I have looked in the 7 different GBPVRRecordingService.exe.log logs and don't really know what to look for. I am recording from a single PVR150 OTA signal coming from a coax cable. Anyone figure this out yet?