[fysiks]

I doubt it has anything to do with them being on the same host as they use different protocols (fast download uses HTTP and the server does not) provided that your host is properly configured for both purposes and can handle the extra processor power required. It's not generally recommended to do this though.

In your console (of the client) turn on developer (developer 1) and then join the server. This should output more info to your console about connecting to the fast download server IIRC.