When is a payment marked for Withholding

Here is a scenario

1. Supplier is created on 9/21 and is not marked for withholding

2. PO is created on 9/21

3. On 9/28 Supplier is updated and is marked for withholding

4. On 10/1 voucher is created & Matched

5. On 10/28 Voucher is paid

on 1/14 run the 1099 mismatch report and the voucher appears as a mismatch. Is this because the PO was created before the supplier was updated to withholding?

Thanks