Don't remove all of your error documents. I didn't even realize that it was a 404 error causing it the redirection. I thought it was a referrer problem. But, since we're on the subject, on any domain you submit free sites from you definately want a 'friendly' 404 page, not a big ad. That way, if a link list's bot catches one of your pages 404ing, they won't ban you thinking that you did it intentionally.
The above 404 is no fault of your own. A comma got put at the end of the quoted link and caused the 404.