Supplier name coming in PO action history. Please help figure why

HEllo All,

I am using following api to send a PO to Approved status after it is updated (requires reapproval)  by a pl sql code (updates line promise date)

IF v_ship_date IS NOT NULL THEN

        --the below po_change_api1_s.update_po will not work if Promised date coming from

        --vista is null

        fnd_file.put_line(fnd_file.log,

                          'Promised_date is not null so calling po_change_api1_s.update_po to approve the PO: ' ||

                          v_po_num);

                            fnd_file.put_line(fnd_file.log,'sourabh coded getting called' ||

                          v_po_num);

        l_result := po_change_api1_s.update_po(x_po_number           => v_po_num,