You're having some issues with your board setup. The
forumhome/forumdisplay templates have likely been customized, but something isn't right. Like when you collapse one category, only the first forum in under the category disappears.
I assume your trying to get the little subforum list that appears under some forums? In order to get that, they have to be subforms of whatever forum their under. Meaning, if you have a category set, and a forum under it, then only subforums of that forum will show up as the little list on the forum home page.
Category
-Forum
--Subforum
But with that said, you should take a look at your templates and make certain that they haven't been modified incorrectly.