IE8/IE9 Copy/Cut/Paste doesn't work on cross-domain IFRAME in Showmodaldialog window

I am using showmodaldialog to open a new window. My pop-up window contains an IFRAME which points to cnn.com. When I open this pop-up window cut/copy/paste doesn't work even though these functions are enabled on right-click. I am trying to paste a word from clipboard to CNN.com search textbox.

It works fine if I open pop-up window in my own domain but doesn't work in cross-domain. I checked all the settings in IE and I couldn't find anything.

Can someone help me figure out what is the problem?

Here's a code snippet.

*******************************************************

a.html

<code>
<script language=javascript>
function doit()
{
var sData = "";
var sFeatures = "center:yes; dialogHeight: 800 px; dialogWidth: 900 px;";
var returnvalue = window.showModalDialog("main_frame.html", sData,sFeatures);

}

function openit()
{
 window.open("main_frame.html");
}
</script>
<a href="javascript:doit();">Click This For ShowModalDialog!</a>
<a href="javascript:openit();">Click This For open!</a>
<iframe  src='http://localhost/web/f1.html'  ></iframe>
</code>

******************************************************

main_frame.html

<code>
<table width= "100%" height = "100%" border = "solid">

<!-- <tr width= "50%" height = "50%">
<td width= "200px" height = "200px"><iframe  src='http://localhost/web/base/logindisp?tenant=DS_MP_1' ></iframe></td>
</tr> -->
<tr width= "50%" height = "50%">
<td width= "100%" height = "100%"><iframe  src='http://localhost/web/f1.html'  ></iframe></td>
<td width= "100%" height = "100%"><iframe  src='http://www.cnn.com'  ></iframe></td>
</tr>

<tr width= "50%" height = "50%">
<td width= "100%" height = "100%"><iframe  src='f1.html'  ></iframe></td>
</tr>

</table>
</code>

********************************************************

f1.html

<code>
<input name = 'test'/>
Ignore this.
</code>