JQuery: getResponseHeader not working in IE when used inside an error function

I am using jQuery 1.7.1. along with the Ajax Form plugin , the latest version is available. When I make an Ajax request, for example:

$('form').ajaxForm (
{
    success: function ( data )
    {
        alert ( data.responseText );
    },
    error: function ( data, status, error )
    {
        alert ( data.getResponseHeader('Content-type') );
    }
}
);

If the request returns an error, IE (IE9, in my case) will always return undefined for the Content-type header or any other header. The data.responseText property also returns null. This does not apply to Gecko or Webkit browsers.

This is an example of response headers returned by an Ajax request:

Response         HTTP/1.1 400 Bad Request
Date             Fri, 18 May 2012 08:15:32 GMT
Server           Apache/2.2.14 (Ubuntu)
X-Powered-By     PHP/5.3.2-1ubuntu4.15
Expires          Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control    no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma           no-cache
Connection       close
Content-Type     text/html

Any idea on how to get around this behavior in IE?