This was an issue of the original server that hosted the content. While the page displays 404, the header was serving the Wayback Machine with a 200 OK response.

This is one of those cases where a company hired someone who doesn't know how to generate proper headers in response to browser requests.

See http://archive.org/wayback/available?url=http://www.malliss.de/Geschichte/Muehle/Muehle_gross/muehle_gross.html

In these cases, it's easier to just go to https://tools.wmflabs.org/iabot/index.php?page=manageurlsingle&wiki=dewiki, look up the original URL and delete the archive associated with it, or find a better one to replace it with. IABot supports 22 different archiving services so it can handle almost any archive URL you give it.

I have no deleted the archive from the DB.

Thanks