Purchase Order - Partner functions and Address

Dear all,

I need your inputs on the below requirement.

When creating PO (ME21n), we have requirement that OA Vendor's address has to be displayed on the Address tab instead of default VN Vendor's address. I have achieved this requirement using the BADI. But when the users to the Partners tab and change the OA Partner and come back to the Address tab, it's still referring to the old OA vendors address (still we are in the PO create). However if the save the PO, I have handled the logic to update the address to the new OA vendors address. But the requirement is after they change the OA vendor if the come to the Address tab, the address should be reflected right away. I'm not exactly sure where to handle this code. Any help is much appreciated.

Thanks,

Justin.