PO Req to PO Attachment Copy - Duplicate Document ID?

When AutoCreate is used to create a Purchase Order from a Requisition, the attachments are copied from the Req Header and Req Line to the PO Line.  When this happens, is it intended functionality that the document ID is re-used on the new PO line attachment records or should each attachment that is copied also get a new document ID?  I'm seeing both results at two different clients and I cant' find definitive documentation as to which is correct and intended.