Form tag does not get added in Chrome and Opera

Form tag does not get added in Chrome and Opera

I have a button on my form. When I click that button I first ajaxpost to a webpage on the server, take inner html of the specified div and finally append that html to another div that will present a jqueryui dialog. Here's the code:
  1.     $('#window').html(content).
  2.     dialog({
  3.         title: title,
  4.         show: 'drop',
  5.         hide: 'drop',
  6.         width: 400,
  7.         buttons: buttons,
  8.         position: { my: 'center', at: 'center', of: window }
  9.     }
  10.     );
And here's the inner html of the div on the posted page:
  1.       <div id="cardOrder" class="cardOrder-div">
  2.             <form runat="server" id="frmAjax" >
  3.             <table class="cardOrder-tbl">
  4.             ......
  5.             </form>
  6.       </div>
I have a problem with Chrome and Opera. When I click the button for the first time and show the jqueryui dialog with the above html content, the "form" tag is missing. But the next times when I present the dialog the form tag gets added. And if there's no form tag I cannot submit. Firefox and IE lack this problem. The form tag gets added right from the first dialog show.