AP Voucher Logging - Partial Match to a PO Closes the PO and Amount to receive goes to 0

We are implementing AP Voucher Logging. During our testing the user had a PO for $5000 and entered a Voucher for $1000. After the Logged Voucher was approved and trying to match to an order. The user got the Amounts don't match error, and then changed the lin on P4314 to match the voucher. Opt field has a 1. So the amounts match and the voucher processed. Then we look at the PO and the lines are closed.

The processing options are set to status 400 and cancel PO is 999.

Can someone give me the correct procedure for doing a partial voucher to a Order?