Doing a manual retune did the trick, as suggested.
I never usually bother with the non-Freesat mode, but I had originally done a manual tune when I first had the HDR, just to see what was there. Now though, I have a need to be able to watch STV next Monday night after my recording of Case Sensitive (Part 2) got dumped by 'a recording with a higher priority'. I hate those conflicts; I never know which one to cancel, if any. It usually sorts itself out correctly, but not last Tuesday; CS was aborted in favour of the just-finishing recording on BBC2. Grrrr!