The main category is not used for storage of blogs. It's just a container for the blog categories. The user should not be able to select the main category as their blog category so am unsure how they managed to add blogs to it.
How can I correct this ?
You can't, it's working as designed. I suppose you could opt for not selecting a top level category then use the Exclude category feature to exclude all your other categories except the main category and its children. This should allow them to store to that category and allow the display of blogs in that category on profile.