I think this is the first Listener I've ever done in 30 years where I've guessed the theme right before even starting, but that didn't make it any easier. Seems like extra letters in clues is the new rock'n'roll - and it made for a hard solve. At least I had a good idea of what one of the extras would be in each case, which helped.
As A Hearer says, the four-letter entries were tricky, especially 2 across. I spent ages on this and although I should have seen the wordplay sooner I'm not at all convinced by the definition. 18 across was quite easy by contrast but - purely as a matter of taste - I don't consider the removed item thematic!
Haven't got the highlighting yet, so I'll have another look tomorrow. I'm reassured by the posts so far that this isn't like the highlighting in The Puzzle I've Promised Not To Mention...