Here in the UK I've got access to digital TV through my set top box. I generally watch TV this way but occassionally I'll watch terrestrial TV and either leave the digi box on, usually to tape whats being broadcast.

However, there is one draw back to this in that, for example, if I'm recording a decetive drama off ITV3 every time there is a start or end of a commercial break the TV switches from the terrestrial channel to the AV channel that I use for the digi box. This is a pain in itself but it always seems to occur at important plot points, female nudity etc etc on the terrestrial show.

Why does this happen and is there anyway of stopping it?