This problem occurs in all the themes I have tested: Daily, Scholar, Product and MU. It occurs when using a preset style. However, the problem disappears when I use BuddyPress Default.
I have all the latest software, including the recent update to Daily. I have a clean installation, only a few weeks old that I am still getting ready for prime time. I have only 2 plugins: BuddyPresss and Askimet.
I inserted 10 categories, each with sub-categories. Some categories and sub-categories have spaces in the names but the core names all have dashes where the visible name spaces occur. Besides, this problem occurs independently of whether or not the category name has spaces.
I have one post, simply named Post, that designates all categories. I did this to make all categories display their names. I have two additional posts, one each in categories 1 and 2. I added all posts using the admin backend.
Of the 10 categories, this problem occurs only in categories 2 and 3. It also occurs in all the sub-categories of 2 and 3.
The test is simple: click on a category and wait for it to display its one or two posts. All categories display their posts except categories 2 and 3 and their sub-categories.
Based upon the above, I think there is a fundamental problem in all the themes that is not present in BP Default.
You can test this at http://usa1buzz.com/