title: 2 window.parent.onscroll calls on page do not work
body: <p>I have an HTML page with 2 iframes within it. I want each iframe to display the Y scroll offset of the <strong>parent</strong> window. One iframe works on page load, the other does not.</p>
  
  <p>The parent HTML page just has the iframe embeds. Here is the code running in the iframe:</p>
  
  <pre><code>function run(){
      document.write("&lt;div id='scrollY' style='float:left;'&gt;&lt;/div&gt;&lt;br&gt;");
      scrollY = 'no';
      document.getElementById("scrollY").innerHTML = scrollY;
      window.parent.onscroll = function(){
          scrollY = window.parent.pageYOffset;
          document.getElementById("scrollY").innerHTML = scrollY;
      }
  }
  run();
  </code></pre>
  
  <p>The result on load and a scroll downwards will display something like:</p>
  
  <pre><code>iframe1 = 100
  iframe2 = no
  </code></pre>
  
  <p>Can I only call <code>window.parent.onscroll</code> once? This doesn't seem right to me.</p>