Marketpress stored information

I have been having quite a number of difficulties with your plug-in. Numerous Line 1 errors, etc. The latest is the plug-in is seemingly storing information from the last user to checkout and showing it to the next user. Not sure if this will replicate with this link or not, but it happened to me also... Click on the credit card icon and the name and address of the last shopper appears.
https://www.1040education.com/store/shopping-cart/checkout/
Please help. This is not cool at all.