I think (I hope 
) I’m starting to understand.
When you unread a topic, you’re redirected to the home page but the now unread topic doesn’t go into the Unread tab unless you force a page reload.
Is that the issue?
I would also expect the topic to appear without reloading the page.
I believe the timing request with the last=1 query string sets the unread state. The home page is loaded immediately after and should put the topic in the Unread tab, however, for some reason, it doesn’t.