Apache2 w/ proxy balance and Rails: 404 error

Hi, I'm using proxy balancer to pass requests to a cluster of mongrels. When I try and access a non-existant page I get back a page with a text header, then the html of the correct 404 page. The browser renders this page as plain text. If I bypass apache and hit the mongrels directly on their ports I get the correctly rendered page.

Any suggestions?

Thanks, Rob.