EDI 810 Invoice Customers with an AltBillto does not set EDIReady

We are using a data directive to generate a file that we send to our VAN. It uses a condition to check the value of the InvcHead.EDIReady field, then runs some custom code to generate the delimited file based on rules setup in the UD03 table. To get the EDIReady field to set true the Auto Invoice / ERS Order checkbox in the Billing/Detail Tab of Customer Entry needs to be enabled. An outbound document of invoice needs to be also setup with a value in the Alt Trading partner field.

Following the value of the OrderHead.EDIReady, ShipHead.EDIReady and the InvcHead.EDIReady flag. I can see that the EDIReady is only set to true in the InvcHead table once the order has been shipped.

I’v found that if a customer has an alternate Bill To setup, the InvcHead.EDIReady flag is not set to true. What I see in the custnum of the failed invoice is the custnum of the alternate billto customer, which is expected, working invoices have the custnum of the base custnum.

What I don’t get is if I setup the customer that is the AltBill to with all of the EDI settings it still does not set the EDIReady flag to true.

Am I doing something wrong, a configuration perhaps, or is this a potential undocumented feature?