Nice spotting :)
this doesn't work for me, firstly this line of code for me is on line 582.
When i change this bit of code i add to cart, fill in details, choose payment and when i clock confirm i get time out 500 page. It does work if i copy over the WHOLE orders_model.php but that changes my order of the order values (sub total, discount, deliver then full price)
What do you suggest?