On my beta site, I did some shopping while logged in as Admin. During that time I viewed my cart.

Then, I created a different user called Shopper. When I am logged in as Shopper, and click on View my Cart, I am directed to Admin's cart.

At first I thought this was a cache issue. So, I cleared my site cache, and my browser cache. I logged out, logged back in as Shopper, and I can still see the Admin's shopping cart.

In addition, when logged in as Shopper, I added a donation to the cart. This donation was added to Admin's cart...or Shopper's cart, with all of Admin's stuff in, depending on how you look at it :)