I've noticed that when I make the first line of my post
Hi Superuser,
or
Hello Superuser,
It auto-deletes it.
If it is anything else (maybe a few more variants of this exist), it will not delete. Is this intentional?
Salutations are automatically removed, because posts do not need to have salutations. You can see the full regex used to select salutations to remove in the linked meta SO post.