Just out of curiosity, I marked a topic disregarded - and from that point onwards it was shown as 'unread' in the message index of the board in question.
I'm pleased to see that marking the board (or everything) read doesn't clear the disregard notice (as could happen with the hack I made, though in theory it shouldn't!), but I think it's counter productive to have a disregarded topic as always be shown as unread, whether it is or not.
Yeah, that's my fault, I know the bug since...quite a long time, but never remembered to actually fix it... :-[
Tracked ... https://github.com/elkarte/Elkarte/issues/252
Funny, I didn't notice before, but this topic and the related issue have the same id!
Darn, I should have waited 252 days to fix it! :P