Mystery solved re NTL Virgin Media box!
About 5 years ago I had a Genius 815 (http://tinyurl.com/c5guob8) and I got that sucker working with everything, TV, HiFi, PVR - even a custom Dbox2 decoder - but would it talk to the NTL box? If it felt like it! I'd sooner it not communicate at all than the half assed way it almost did, just the way you describe.