Hi Les - I don't think 12a was an anomaly on your part, I think the onus is on the solver to sort it out and the answer to 4d provided me with the opportunity to challenge what I had put, I just didn't see it straight away.
I have seen your other puzzle and in fact have just finished it. I liked the clue to 9a. The theme was a good one for me and in fact I got 4d as my first answer and the linked ones I got reasonably quickly. I've just remembered that you said you called it 'red herring' and asked the question why? I can't immediately think of a reason unless it is that the linked clues aren't as directly linked to 4d as you might think when you get the answers.
Cheers for the crossword - I'll have to get back to doing the ones I normally do!