Im not able to replicate this on my dev system or the www7 test portal. Do you have any errors in your dnn event viewer? The issue must be something with your cart install possibly something with your cart install has gotten out of the sync. I recommend that you install the latest version of the cart on a new dnn install on your laptop to test or you can login to our test site http://www7.smith-consulting.com/ and verify its working.
Please send an email to support@smithcart.com if you need a login.