The usual cause is double-posting. Submit the comment form twice accidentally, see two copies of your comment, delete one, now you see one copy and leave. HN au

The usual cause is double-posting. Submit the comment form twice accidentally, see two copies of your comment, delete one, now you see one copy and leave. HN auto-killed the duplicate, but your own comments never appear dead to you, only to others -- so you end up deleting the copy everyone else saw, while leaving only the dead one.