jQuery 1.3.2 update to 1.4.2 : ifModified option doesn't still work.

jQuery 1.3.2 update to 1.4.2 : ifModified option doesn't still work.

Hello,

I got a problem which I can solved by myself.
I got a very simple AJAX script which doesn't still work since I change my Jquery version.
It seems to ignore "ifModified:true" option and continue to append content in my page.

index.php
  1. <!--<script type="text/javascript" src="jquery-1.4.2.min.js"></script>-->
  2. <script type="text/javascript" src="jquery-1.3.2.min.js"></script>
  3. <script type="text/javascript">
  4.     function refresh(){
  5.         $.ajax({
  6.             url: "loaded.php",
  7.             ifModified:true,
  8.             success: function(content){
  9.                 $(".result").append(content+'<br/>');
  10.  
  11.             }
  12.         });
  13.        
  14.         setTimeout(function(){
  15.             refresh();
  16.         }, 3000);
  17.     }
  18. $(function(){
  19.         refresh();
  20.     });
  21. </script>
Loaded.php
  1. <?php
  2. //header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
  3. header("Last-Modified: Sat, 26 Jul 1997 05:00:00 GMT");
  4. echo gmdate("D, d M Y H:i:s");
  5. ?>

Could you help me, I have no more idea.
(Excuse my English, I'm French)