With reference to original post:

1. if you are already logged in to DNN when you place an order, and the user doesn't already have a customer record, the customer that is created for the purchase is not linked with the logged in user. The DNNUserName field set of the customer is set to the email address, but no DNN account is created. Every time a purchase is made, a new customer account is created.

Now, for user account that already exists with no customer record, if logged on, no customer record is created. If not logged on, the user is unable to log in using the Cart login page. Free products do not present the login page, even if login is required in the General Cart configuration.

If you register a new user during checkout, firstly address details are picked up from a previously logged in user!!. Secondly, login fields are (confusingly) presented at the bottom of the confirm order page. When you enter the details you entered on the registration page, they are not accepted, and (in my case) failed password validation, although previously accepted. In any case neither a DNN user nor a customer record had been created at this stage, so authentication wouldn't be possible.

1. No customers show up in the Manage Customers screen

Still the case

1. The Catalogue Show Options button (/DesktopModules/Smith.BuyNow/images/options.gif) is missing from the package

Still the case

Have to add the back button not working on the Order Processed Confirmation page to that list.

Please copy the attached dll to your \bin folder to fix the following issue:

if you are already logged in to DNN when you place an order, and the user doesn't already have a customer record, the customer that is created for the purchase is not linked with the logged in user. The DNNUserName field set of the customer is set to the email address, but no DNN account is created. Every time a purchase is made, a new customer account is created.

Reset iis after copying the dll

Nope, still doesn't work. You're storing the user's email in the DNNLogin field in the customer record, which is not the same as the username.

I am also still seeing this error, even in 2.84.00, but I see if from the "Print Invoice" link on the Order Details page as an admin, coming from Manage Orders.