Selection of vendor alternate address in a PO.

Dear All,

We are creating a PO, the vendor has multiple addresses(Primary-Delh, Hyderabad) defined in vendor details form. In PO we need to select the secondary/alternate address. We have tried selecting the copy to address option at PO header setup->Alt address->vendor tab but by doing so, the delivery address get’s changed. Can anyone let me know how to select the alt address.