Ah well, the rejoicing lasted about 3 days then - predictably, Fetch TV have introduced a nasty new bug in the latest firmware that a lot of people will hit. It seems that recording two programmes simultaneously will often only record one properly (immediate symptom is that one of the two recordings fails to have a red blob next to it - almost as if the software pressed stop on one of them at the start).
When the failed recording is played, it wil display a blank screen, pause the playback and put up a length time of 0 minutes and 0 seconds. No amount of keys seem to resurrect the playback either. It happened with me when recording a mix of one HD and one SD programme, but I guess I'll try other combinations and report back here (yes, I did try to "restart" the second recording either via the EPG or via the Record button, but all that did was end up with a load of zero-length recordings - one for each resumption attempt!).
AVForums.com users have also seen this bug, so until Fetch TV fix this, I would either advise you to downgrade to the previous stable release or avoid simultaneous recordings. I'll see if I can report this to Fetch TV's dreadful ticketing system.