XMLHttpRequest populates responseText with 301 Moved Permanently intermediate content

import QtQuick 2.2

Item {
  Component.onCompleted: {
    var ajax = new XMLHttpRequest
    ajax.open("get", "http://path/to/the/script/below")
    ajax.onreadystatechange = function() {
      if (ajax.readyState === XMLHttpRequest.DONE) {
        console.log(ajax.responseText)
      }
    }
    ajax.send()
  }
}

<?php
    if ($_GET["test"] == "yes") {
        echo "But this text should";
    } else {
        header("HTTP/1.1 301 Moved Permanently");
        header("Location: " . $_SERVER["PHP_SELF"] . "?test=yes");

        echo "This should not be part of the responseText";
    }
?>