NodeJS - "This type of response MUST not have a body..."

I've recently ran into a very interesting problem while writing a web app with node.js. Essentially, all I am doing is serving the index.html page to the client.

Here is the code:

var http = require('http');
var url = require('url');
var fs = require('fs');
var util = require('util');

var server = http.createServer(function(req, res){
        var path = url.parse(req.url).pathname;
        if(path == '/'){
            console.log("LOADING INDEX...");
            openIndex(req, res);
            console.log("LOADING COMPLETE.")
        } else {
            res.write("Something went wrong...");
            res.end();
        }
    }
);

var openIndex = function(req, res){
    fs.readFile('./index.html', function(error, content){
        if(error){
            res.writeHead(500);
            res.end();
        }
        else{
            res.writeHead(200, {'Content-Type': 'text/html'});
            res.end(content, 'utf-8');
        }
    });
}

I've put some debugging statements just before and after the index.html page loads: "LOADING INDEX..." and "LOADING COMPLETE".

Now, I have shared the link to my server with my Facebook friends so they can see my app. Most of the time, everything works as it should, but once in a while I get this error:

LOADING INDEX...

This type of response MUST NOT have a body. Ignoring data passed to end().

and just now I've also gotten:

LOADING INDEX...

This type of response MUST NOT have a body. Ignoring write() calls.

The process never raches the "LOADING COMPLETE" statement.

I've tried to reproduce this countless times (accessing my app on different machines, browsers, devices, OS-versions) but every time it works as it should. I've looked around for other people having this problem, and it seems that somehow, a body is getting into a GET response? I'm not entirely sure what this means or how to fix my code to prevent that from happening. Also, I'm not sure what the clients that produce this error see? Do they get to see my app? (i.e. are these just warnings and as far as they are concerned everything is fine?)

Any help with this will be greatly appreciated.

Xaan