Negative Cart Id cause order become backorder

It was occurred for CS-cart 2.0.15 under PHP 5.2.13 environment.

As I knew, some of Hash option combination index will be became negative under PHP 5.2.13.

I met Negative Cart Id cause order become back order 1 month ago and contacted support on that time, but only got 1 repair trial pack. As I tried the trial pack, modified the fn.common.php, and the PHP error when visit the site. This problem still on hold with support for 2-weeks.

My problem is that some of items will have Negative Cart Id after add to cart. If just those items. the orders are successful processed. When with other regular postive cart id items, it may cause order become back order after place order.

Any one has better suggestions to fix this bug?