onDomReady problem with IE

onDomReady problem with IE

In our webapplication we're using an overlaying Div to prevent users from sending a submit before site is loaded completely.
To do this we use the DOMContentLoaded-event of webbrowser. When DOM is completed the Div should disappear and user can start working.
Everything works fine in Firefox. Because IE doesn't support the DOMContentLoaded-event we use the defer-attribute for a script, which is loaded at the end of page.

Following sourcecode is used:

domready.js:

   window.onDomReady = DomReady;

   //Setup the event
   function DomReady(fn)
   {
      //W3C
      if(document.addEventListener)
      {
         document.addEventListener("DOMContentLoaded", fn, false);
      }
      //IE
      else
      {
         if(document.all)
         {
            document.write('<script type="text/javascript" defer="defer" src="ie_onload.js"><\/script>');
         }
         var oldLoad = window.onload;
         var newLoad = oldLoad ? function(){fn.call(this);oldLoad.call(this);} : fn;
         window.onload = newLoad;
                               }
         }

ie_onload.js:

         hideModalDialog();
               
In page-source the domready.js is loaded in header. In body following code shows up the overlaying Div and setups the defined onDomReady-attribut to hide the Div:

   <script type="text/javascript">
         showModalDialog();
         window.onDomReady(function(){hideModalDialog();});
    </script>
               
Now the problem: In 100% of loading pages in Firefox the page is loaded correctly and the Div disappears after loading. The same works fine in IE, but in 0,01% of all loadings the Div
never disappears and user can't interact. The statusbar shows "Done" for page. When reloading the page the site is loaded correctly. We use a template system and the code for showing and hiding the Div is included everywhere. But the problem can't be located to a single page it appears randomly and is very hard to reproduce.
Newest investigations show the problem appears more often when loading sites in low-bandwiths e.g. UMTS.

In former versions of our DomReady-function we used the .onreadystatechange instead of defer-attribute but the loading-problems had appeared more often.
We need a solution for all versions of IE >=Version 6.