Landed cost voucher is not working if PO is manually closed

I created a purchase order for 100 quantity. I received 60 qty and the supplier told me that he won’t be able to deliver the balance stock. So I closed the PO manually and created the LC voucher for the received items. But the system is not allowing me to submit the LC and showing the message that the PO is closed. I reopened the PO and then I was able to submit the LC. Is it a bug or any reason for the same?

This is the nature of PO & SO.