Deleting not possible - Open Order exists

Hi

I am trying to delete a secondary location which has no commitments and no quantity on hand, I receive an error message, delete not possible - open order exists.  When I investigate I find that there is an open purchase order for the item in question but the location is the primary location on the purchase order detail and not the secondary location.

Why I am not allowed to delete the secondary location, It seems that the validation is being done on the item branch combination and does not take the location into account.

I need some clarity on the validation of open purchase order.