Discounts on SO Invoices (without sales order)

We are using R22 only thru update 104.  When I create a sales order invoice for customer without an underlying sales order, the Discount g/l code used when the g/l batch is created is the Sales Account ID from the customer, not the discount id from the customer.  If i create a Sales Order, then prepare an invoice and then post it, the g/l code is correct, the customer's discount account id.  

Seems to be an issue in the SOInvoiceEntry graph where the system is not correctly handling a null value for sales order type (there is none).  

Has anyone else experienced this and how did you fix?  Am I way down a rabbit hole for no reason?