I added multiple new Product Categories and changed multiple products, however Product Categories tab still shows product that was moved to another category.

Example: 

Product A was assigned to product category All/Saleable

Product A was changed to product category All/FG/Sales

If the user looks at Master Data > Products > A, the individual will see that A is assigned to Product Category All/FG/Sales

If the user goes to Configuration > Product Categories, for category All/FG/Sales, the TAB in the right corner represents the correct product assigned to the new category. However, if the user goes to Configuration > Product Categories, for category All/Saleable, the same product is assigned there as well.

How can a product be assigned to two Product Categories. This should not be possible.