What are the implications if Multiple Disposition Codes are used on a single RMA record?

We require three transactions for exchanges:

Purchase Order to Receive defective item

Replacement Order for defective item

Credit Order to reverse the invoicing of the Replacement.

Our organization has chosen not to use the Advanced Exchange functionality therefore we must have two Disposition Codes (RMA Line Types).

Ideally all transactions would be entered/created under a single RMA record for a streamlined process rather than created two separate RMA records.

We have been able to successfully create an RMA with a single Disposition Code, save the record and then add a second Disposition code.

However, we receive an error (code = 40R1- Disposition Code Invalid when two different Disposition Codes are entered) when we attempt to add both codes during initial creation of the record.