I had run into this problem years ago (BM 2), and it was something
simple, but I don't remember the solution.

Server running NW 6 / BM 3.7 and Apache hosting the company web site
on public ip address.

In general, all works fine including the mini-web server. I get to
403 forbidden messages, 505(?) Gateway timeouts, and some other error
messages from the mini-web server just like it should when called for.
However, if you type in a wrong url (something that does not exist -
like www.asdfghjkl.com), I get the company web page (that is hosted on
the BM server by apache) instead of an error message. I've ignored
this for a while now thinking some day I'll remember what solves this,
but no luck. And now I'm trying to resolve a problem with a remote
web site, and this is annoying me when I want to see the errors. So
now I need to fix it. Anybody run into this in the past and remember
the fix?