Proxy requests are sent with port number, even when no port is provided

[hollsk]

In app.js, specifying a route with no port number like this:

 "/^\\/blog/": {
    "host": "root.webservice.lh"
},

results in requests being proxied like this:

Proxying request for localhost:5400/blog/post1?shunter=1455219839081 to http://root.muncher-webservice.lh:80/blog/post1?shunter=1455219839081

If I don't specify a port, I'd expect one not to be sent (:80 is already implied in the absence of a port being explicitly provided).

Is this a bug, or is there an undocumented configuration setting I'm missing somewhere?