I don't think it's your mistake. It seems HN automatically removes certain leading/trailing words from titles so as to reduce clickbait but it doesn't seem to be very smart about it.
I'd be much less annoyed by it if dang finally made it a pre-submit check (maybe with a checkbox "Overrule") like the "too long" check. But no, it seems to be important that the submitter has to check manually whether the title he just typed in is still there.