I haven't figured it out yet, but at some point the Staff CP Manage categories page will update itself and match other other pages.  Hopefully, you can get this corrected to update the Staff list as you add categories.

To reproduce, click the "Add Category" button on the Staff/StaffManageCategories1.aspx page, then add the category, and as you go back to the manage category pages, the list does not show the category you just added.