I've been playing/testing this and there is definitely something strange occurring, but I can not find a logical explanation.
Yes, each NEW entered rule gets a new sequential "404_id". But the row does not always get sorted to the bottom in the table. Rather than try to explain in detail what I experienced, I will suggest to create a sequence of rules. Then start deleting some, then renaming some, and then adding new rules, and finally add some of the original rules back in. If you do not get strange results, please let me know, and I will gladly show you what I am seeing.