I found that I can update the cart with a negative number so the total is a negative number. If I click through to submit the order the system blows up. Is there a fix for this? I don't think the cart quantity should go negative. If I shop at, for instance, Staples.com, I add something to my shopping basket and then try to put a -10 and update the quantity, the negative amount is ignored and the original quantity shows up again. If I put the quantity to a lower positive number, the value is updated.