Is something causing the camera to turn off? Might something be sending an "off" command to that camera?
If it is triggered by a motion detector, then perhaps when it sends the "off" command after motion stops, it turns the camera off. AHP doesn't know what's coming in through the VA11A, it just knows when you tell it to record, and when you tell it to stop.
You can verify what's going on by splitting the video output from the camera off to a TV or VCR, and monitoring it at the same time.