Items of same option name in cart being replaced when adding another option value

Hello,

-----Zencart Information-----

Version of Zencart: Version 1.3.8
As far as I know, the site has not been upgraded, though I am a new developer to the account. It does not appear to have been upgraded
No addons appear to be installed on the site.
The site has been customized.
The issue does appear to be a layout problem.
The issue does not appear to be related to the hosting company.
I am unsure what to search for exactly in the FAQ, though I have done some research on google, to no avail.
The problem started since the first install, and has always been an issue.

The issue is that when I have an item that has multiple attributes (3 different sizes, etc), I add one item with size X to the shopping cart, and its there. Then I add the same item with a different size to the shopping cart and it replaces the first item.

Test URL: http://67.199.55.197/dev/index.php?main_page=product_info&cPath=124&products_id=83

Is there a way to correct this? Do newer versions of Zen Cart correct this?

Thanks,
Sugi