nodejs + express strange things on different ports

Can someone tell me what is going on? I have an aplication:

var express = require('express')
  , http = require('http')
  , app = express()
  , port = 3000
  , mw = require('./lib/middlewareView')

app.use(mw());

app.get('/', function (req, res, next) {
  res.send("hello");
});

app.listen(port, function() {
    console.log("Listening on " + port);
});

and /lib/middlewareView.js :

module.exports = function middlewareView(){
  return function middlewareView(req, res, next) {
    console.log("middleware run");

    next();
  };
};

When I'm using port 3000 and open http://localhost:3000/ everything seems to be fine. console output:

Listening on 3000
middleware run
hello

But if I switch to port 5000, console prints this:

Listening on 5000
middleware run
hello
middleware run
middleware run

So the middleware runs 3 times during one request, right? Is it normal?