Open sub-contract POs with job closed

I found several open POs with sub-contract operations where the job was closed. The PO should close when a receipt is entered for the full amount. In these cases, there was only one line, one release, and it was received complete, yet the PO remained open. I know that sometimes if they enter a receipt, then reverse it, or maybe the PO changed in process that that could result in a PO staying open. But that’s not the case here.

Has anybody else seen this? Any idea why this would happen. If it was just one or two, I would overlook it, but there were 30 such POs.