Wrong new status of subforumlink on index

I have a board like this

Category
--Forum
----SubForum
-------SubCategory
----------SubSubForum

When the SubForum is showing on the Index as Subforumlink, it allways stays read, even if there are a lot of new Posts in the SubSubForum. When I delete the SubCategory and have my SubSubforum direct under the SubForum everything is okay and the SubForum is shown as unread. But I need the SubCategory, too.

Hope that can be fixed and it's really a bug and I am not just too stupid to manage it right.