If you have no padding, then the Humax will use AR (Accurate Recording), in this mode the box turns on 15 Mins before the EPG start time and looks for a start signal transmitted by the broadcaster before recording will start. The BBC channels don’t normally have a problem with the AR signals, however the other channels (especially Channel 5) have been known to ‘forget’ to transmit the start signal. I would try padding, say just 2 mins at the end, this will turn off AR, just to see if it solves the problem