the url when I go from the shopping cart to the checkout page the url that is set first time is mysite/index.php?main_page=checkout

on a refresh of the cart and then click through it becomes mysite/index.php?main_page=checkout&fecaction=null this takes the user through to check out. What is causing it to set the &fecaction=null part of the URL and therefore get through to the correct page. Whis is it not going through in the first instance.