Should a user be able to edit a partially sourced requisition?

We are on 9.2 Image 8. We upgraded a few months ago from 8.8.

We are using ePro to enter requisitions and Add/Update POs to manually create POs from special request requisitions. End users (requesters) enter the requisitions, and buyers make the POs. When a buyer makes a PO from a requisition, and then reduces the quantity and/or amount, they are supposed to finalize the PO. This returns the unused pre-encumbrance to available budget and also changes the req line sourcing status from Available to Complete, so the unused quantity cannot be sourced.

In both 8.8 and 9.2, this only works correctly if the finalization and budget-check are done in a specific order. The correct way is to create a PO, copy from requisition, lower the quantity and/or amount on the PO, click Finalize, click Budget-Check, click Save. This results in the req line sourcing status changing from Available to Complete and the pre-encumbrance going back to available budget. The requisition cannot be edited at this point nor do we want it to be.