Virtual server with two different web servers

Can you try to log the request uri and response for me and paste what you get. Something like this...

when HTTP_REQUEST {
    log local0. "Request URL: "[HTTP::host][HTTP::uri]"
}
when HTTP_RESPONSE {
    log local0. "  Response: Status=[HTTP::status] | Location=[HTTP::header value Location]"
}

Otherwise, it could be that you're getting a 302 or 301 response to redirect to the other page. At that point you would rewrite the Location header. If the link to the other internal host is in the response body, you may want to check out trying to remove the "Accept-Encoding" header (see STREAM::expression wiki page or one of the notes on [SOL8115(https://support.f5.com/kb/en-us/solutions/public/8000/100/sol8115.html))