I migrated of Sitecore from 8.0 to 8.1 version. The new version of Sitecore is 8.1.160519 and Commerce Server is 11.3.507.0. All works fine except case, when carts are submitted for processing to SubmitVisitorOrder pipeline. I get exception:
Invalid operation. The Basket object is marked as disposed. This happens if you save the Basket as PurchaseOrder or convert an OrderTemplate to Basket.
I use method SaveAsOrder() of Basket class from CommerceServer.Core.Runtime.Orders for save order (as shown in Commerce.Server.Storefront example). The orders are saved to commerce server, but the basket isn't removed after orders were saved.