I noticed that in the unread page, if i have some "legacy" posts that is unread, and subsequently the category is disabled, it will still remain in the unread page.
However, when one clicks on the post, it will show a 404 error.
I'm not sure if it is a bug or improvement. The Topic/Posts queries and views are highly optimized to show massive amount of data, however the categories views are lacking in this area. We have a movies discussion forum where we create a category for every celebrity and artist whom users want to discuss. After a certain number these pages become incredibly slow to load.