PO Vouchers Post/Paid with Denied approval status

We are on version 9.2. We have approval workflow in place but PO vouchers are automatically approved. I have come across five PO vouchers with statuses that are MATCHED and DENIED.

Accounting entries for the vouchers show:

00009001 - Accural entries posted, will not pay

00021308 - Accural entries posted AND Payment entries posted (not cancelled)

00021318 - NO Accrual entries posted, Payment entries posted (not cancelled)

00021319 - NO Accrual entries posted, Payment entries posted (not cancelled)

00033663 - Accrual entries posted AND Payment entries posted (not cancelled)

First, I don't understand how this happened, and second, I cannot locate the criteria for voucher posting.