no, this is totally broken and has been for years.
1) visit http://kcfdc.org/forum/
(the forum home page)
2) notice dark colored basket for many categories (this means New Posts (unread) within the category)
3) simply go into the category, you don't even have to read any posts, in fact not reading any will only support my point even more
4) without reading a post in the category, use your browser back button to return to the home page. The basket for that category is still bold, yes?
5) reload the home the page or open http://kcfdc.org/forum/
in a new tab.
now you see the category basket is no longer bold, even though there are posts inside that are new and unread.