Supplier user can still edit the PO line even the agreement has been expired

Summary: We hope the supplier user is not able to edit the PO line once we expire specific item in the BPA. However, it seems expiration only blocks the new PO request. It doesn't affect the existing PO. Could you tell us if that makes sense? How can we block user to edit the PO line which the item has already been expired?

Thanks

How to replicate the issue:

1. Set expiration date in the BPA line
2. Supplier user log in the supplier portal
3. Supplier user search out a PO with the BPA we just set expiration
4. Supplier user create a change order to add qty in the PO