PHP built-in webserver throws Invalid request (Unexpected EOF) after every files execution

Question

I'm unable to replicate the bug on anything other than Chrome running linux (14.04), but it has a 100% rate while Chrome/Ubuntu.

Using PHP built in server (PHP -S localhost:43594)

The error is:

Invalid request (Unexpected EOF)

The code I'm executing is this (although it does it with any PHP I run through the local server)

<?php namespace CMS\classes\user;
    require_once "User.php";
    class UserFactory {
        public function create($username, $password = null, $rights = 0) {
            return new User($username, $password, $rights);
        }

        public function delete($username) {

        }

        public function get($username) {

        }
    }
?>

It's important to note that the error occurs about 20 seconds after the scripts execution.