Today, when I try to edit a category, and I discover this problem.
suppose we have some categories, and they're ordered as follow:
and the problem is raised when you edit cate_grand,
when you edit cate_grand, you choose parent of cate_grand is cate_child(or cate_dad), and click Update, and then you will see three categories: cate_grand, cate_dad, cate_child are disappeared, but you still see them in database(table: wp_terms)
Okey, that's the problem I've discovered accidentally.
I hope wordpress team will fix it in next version.
And the last thing I want to say is: sorry for my bad english!
-- LeoLink --