[James2001]

Considering it's been affecting programmes from multiple sources (for example ITV for The Upper Hand and All3Media for Kingdom in addition to the numerous BBC shows), I'm going from the assumption the broadcasters providing the material aren't to blame, as that would mean all three companies are having the same issue, which would be remarkable, it's most likely being caused by UKTV or whoever's preparing the material for broadcast on their behalf.

That BBC commissioning document points out things like scrolling end credits still have to be 50i/50p even on 25p shot programmes because of how juddery they'd be otherwise (not too noticable on Casualty as they're slow scrolling credits, but very noticable on the likes of The Upper Hand and Doctors where they're fast, EastEnders didn't have scrolling credits at this point), but of course this mess is making end credit rollers 25p as well- something which I imagine anyone making a show for the BBC would get told off for, but again it's something UKTV aren't seeing a problem with.

And obviously many captions are well outside the safe areas stated in that document as a result of the zooming in.