Party Specific Item Usage to Restrict Supplier to Certain Items

Hi, I am trying to use “Party Specific Item” doctype in ERPNext to restrict items to a particular supplier.

However, when I set an item to a particular supplier, I am still able to create PO to procure the same item by another supplier.

I am not sure if I have understood the intent of this doctype; but I thought by setting an item to a supplier, I would limit that item to only be purchased by that particular supplier. It apparently does not.

When I try and create a PO with the same supplier and same item, the system also allows it (I’m doing this to see XOR alternative). So I am puzzled as to what this doctype is meant to do.

Hope someone can help me out here.

Thanks in advance!
Mark