Customer Address Different or Incorrect

Greetings - I have a question about how the "customer address" noted in the profile of a customer inside the admin is determined. To clarify:

If I look at a customer by clicking Edit beside his name, I see in the top left corner where it says "Customer Address" there is a completely different address displayed - than the other 2 Shipping and Billing addresses. If I look at his recent order I do see the Shipping and Billing address noted properly and this other "Customer Address" is not mentioned.

Where does that address come from? Is it left over from an old address book entry from his original profile? Is it just left over from when he first signed up and he has since updated his shipping and billing info for these new orders?

This website was recently upgraded to the latest 1.3.9 version of Zen Cart, so I want to be sure this is normal behavior and not something odd occurring from the upgrade.

Customers have an Address Book ... where there could be 1 to many addresses depending on how many you allow ...

One of these Addresses is marked as the Primary Address ... this is considered the Customer Address ...

When making an Order, the defaults start with the Primary Address for the Shippping and Payment addresses, but the customer can then change these to any of the Addresses in their Address Book ...

Thus, you can see 3 addresses in an Order for:
Customer Address - Address Book record marked as the Primary

Shipping Address - Either the Primary or any of the other Addresses in the Address Book

Payment Address - Either the Primary or any of the other Addresses in the Address Book

Thank you, this explanation was helpful. I told my client (site owner) not to worry as long as the billing and shipping addresses appear to be correct on the actual order invoice.