Since setting up this site, we have processed 30 orders via

Since setting up this site, we have processed 30 orders via the MarketPress eCommerce system. Today was the first time we had a glitch with the calculated shipping option. The customer purchased items which should have incurred a $7 shipping charge (the same products in the past have done this correctly). Instead, the customer received free shipping.
I have check all settings (even though they haven't changed) and made sure all plugins are up-to-date.

The website is http://www.savannahtearoom.com

Thanks.