EasyBlog - Primary designation for blog category

I wish to view a post in both categories noted below. What is the purpose of the system designation of a category as 'primary'?

I have two blog categories and when both categories are selected in the composer/editor and the Institute category is set to primary by the system, I can't view the post in the public blog. However when I uncheck the Institute category then save the post - the HMI category is now set by the system as the 'Primary'. The post is now viewable in the public blog. If I again edit the post and check the institute category (both categories checked, HMI is primary) then the post is now visible in both the public blog and the registered users blog.

HMI - public blog
Institute - registered users blog

I have set Institute as the default category for all posting.

1. Open either the default editor or use TinyMCE editor
2. I create a new post
3. By default, the Institute category is checked as an active category and is noted: "Primary"
4. To include the post in both categories, I select the HMI category
5. I also set the viewable field to "viewable by everyone"
6. Save the post and attempt to view the post in the public Blog

See the screen capture attached.

Todd