Tax Codes change when Customer Number changes

 We have a process where we often copy orders. An item goes to a sales rep using one order type and, when the item is sold to an end customer the order is copied for invoicing. 

We set up taxes a few months ago and they are working properly for all orders except a copied order. Originally, when the order is copied, along with the lines, the tax code is the same as the original order. We change the customer to the one that is to be invoiced and the tax code changes to the customer site. 

All of our items, except freight, have a default tax code, which is what we expect to be on the copied order since Product is first in the hierarchy. However, the copied order's tax code changes to what is on the customer site, #2 in the hierarchy. Has anyone else run into this?