drxx -
Interesting that you "... chose to highlight the irregular hare in the grid, fully aware that it was wrong to do so...", as I have done exactly the same with this puzzle!
In my opinion the "hint" is far too vague, as if one expands the area of interest (and why shouldn't we?), then another copy of one of the thematic items turns up, albeit less obvious than the one I believe we are all discussing, but well within normal Listener guidelines. So there are now (I believe) two possible highlighting solutions which would satisfy the requirements, not including the one I have submitted, which doesn't!
But in my opinion this is all a step too far. Highlighting is fine if it helps to define a correct solution or even just indicate that we have all understood the underlying theme. But in this case it's just for show. We have all spent hours getting to the correct solution of the grid itself, but a random extra requirement has then been added with insufficient accuracy, which renders the whole thing fatally flawed in my opinion.
smithsax - I understand your "highlight letters" interpretation, as this also stuck out to me. But how are you sure of where to stop in finding letters? Which of the two possible solutions did you submit?!
Also, unless we ignore the guidelines for submission, as longhare mentioned, then this is all irrelevant. I didn't ignore them!