I'm having a hard time getting answer as to how to properly set up Public Knowledge when using multiple sites and categories. 

We have 3 main categories groups set up with sub categories in each. The main Categories are "Print and Sign", "Nonprofit" and "Small-Medium Business". Each category is assigned to a different site. We have some articles that are only assigned to the Nonprofit category. However, when you search on the site that's using the "Small-Medium Business" category and search using "No Filter", articles that only belong to the Nonprofit category are returned even though they don't belong to that category and specifically say "No Category" in Article Management for "Small-Medium Business".

I've tried editing the Visibility Settings to change from "All Categories" to Custom categories and that doesn't fix the problem. What am I missing? How can I restrict articles that are returned in searches with No filters? Is that the intended result when "No Filter" is selected?

Here are some images of how I have things set up:

here are the data categories. Each Category has children categories and all of them have "All" as the first subcategory.



Data Category Visibility Settings:


I have three sites. Each Site is set up to use a different Category and each site's profiles has data visibilty to a different category:



Here's how an Article is set up and it's only category is "Nonprofit".


When I go to the site for "Print and Sign" and do a search using "No Filter", it returns the article from above that is only assigned to the "Nonprofit" category.



Can anyone help me figure out how to limit the search results to only articles that belong to a specific category? Do I need to set up the categories different? I've tried changing visibility settings and that seems to only cause the filter list to change (as in all of the sub categories are gone).