Category changing itself after adding a new Category

Category changing itself after adding a new Category

I recently added a new Category called "Security", and now a number of existing tickets, even closed tickets, have changed themselves to the "Security" category. It even leaves their existing sub-categories in place, even though the sub-categories do not exist under the "Security" Category. Please help, this is throwing off all of our reporting and statistics, and messing with our incident templates! Running 9400