vim system/helpers/url_helper.php
Change this:
function current_url()
{
$CI =& get_instance();
return $CI->config->site_url($CI->uri->uri_string());
}
into that:
function current_url()
{
$CI =& get_instance();
return $CI->config->site_url($CI->uri->uri_string()). (isset($_SERVER['QUERY_STRING']) ? '?' . $_SERVER['QUERY_STRING'] : '');
}