is_ajax_request does not recognized XMLHttpRequest

You can try this and see what you get this is the old way that we use to do it.

[code]define('IS_AJAX', isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest');

The above (more or less) what CI_Input does

From /system/core/Input.php

PHP Code:

   public function is_ajax_request()
    {
       return ( ! empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) === 'xmlhttprequest');
    } 


I think there is something in the JavaScript that is producing a non-standard XMLHttpRequest.