Finally closing PO does not change CPA amount released

We are on 12.1.3.  Could someone please explain why finally closing a PO does not change the amount released on a CPA?

Example:

CPA is created with amount limit $1000.

A PO is created for $800 that references this CPA, so the amount released on the CPA is $800.

This PO was created in error, so before any receiving or invoicing activity, it is finally closed (I'm not saying whether this is best practice).

A new PO is created for $800 that references the CPA, but it cannot be approved because the amount released is still $800.

Thanks,

Heidi