Cannot delete unwanted PO shipment

A PO was automatically closed when the OSP job was closed.  The buyer, thinking that he accidentally closed the PO, re-opened the PO and added a shipment (SHIPMENT 2) to replace the closed shipment.  The PO's status changed to Requires Reapproval, Closed.  Upon realizing his mistake, he tried to delete the shipment that he just created.  However, each time he clicks the delete button, SHIPMENT 2 gets cleared but another shipment (SHIPMENT 3) gets created.  And this goes on and on..  Would anybody have an idea why this happens and how to resolve this?

Thanks in advance.

Anna