categories disappear after posting when editing

I just did a post and had to go back and edit the categories because I forgot to add one of the child categories into the post.

But when I go down to the categories section and find the parent category, only the ones I’ve used in the child category are there but not the unused ones.

for example. I am using a main category of Minor Leagues. I have about 10 teams listed as a child of that category. I used 4 of them and need to add two more in that I already have but they aren’t there anymore unless I save the post after removing the other categories and then going back and adding them in.