I can’t see them making the stanby for timed stuff only, so I still think it’s a bug.
The aerial unit in the 5026 is a pass-thru device with a channel tuner. It doesn’t re-modulate the signal so there won’t be anything on it to adjust. It looks like, somehow, a signal is getting into your box and causing interference. As I said before - this may even be a signal which is being produced within the box, in which case there is a bad ground, or a design fault.
I have read on another thread (re 5045 box) that people have had trouble on channel 5 and others who haven’t, so it looks like it could be a design fault. I remember reading that some cured it by removing aerial boosters from the aerial path! Don’t know what area you live in but I’ve had no trouble with the signal from the Wrekin transmitter (Telford, Shropshire).
Give an update if you ever hear anything about the Standby situation, and good luck with sorting out channel 5.