For this particular topic:
Every time there is new content, I visit the thread, read it, and then am presented with this ‘old’ unread notification:
This unread topic persists no matter how many times I subsequently visit the topic. It also keeps my unread thread count at (1), which makes me sad.
Not sure that I can provide more detailed repro steps than ‘visit a certain topic with new content, read all new content, experience 1 persistent grey unread post’, but should be able to diagnose what’s going on from my
TopicUser for that topic here on meta.