Fully Received Goods for MFG Lines Reappear in PO505000

Context: We are a project manufacturer that purchases material specific to a project.  We are using Project Stock and Stock Items.

Potential Issue: We are using the Create Purchase Orders screen (PO505000) to trigger purchasing action to satisfy demand coming from production orders.  Below is the behavior we are experiencing:

1. Production Order Demand - Item appears (Expected)
2. Purchase Order Created to Satisfy Demand - Item disappears (Expected)
3. Purchase Receipt Released / Purchase Order Completed - Item reappears (Not Expected)
4. Material Released to Production Order - Item disappears (Expected)

Why does demand reappear when an Item has been received but not released to its production order?  This behavior could potentially lead us to double purchase material.  The purchase order is linked to the production order and maintains the link throughout.  In the Select Materials to Release screen, the system knows is tracking the Available Qty for Project.  It seems this is a missing filter in the Create Purchase Orders screen.   

Am I misunderstanding how this workflow is supposed to function?  Is it possible we have a setting incorrect somewhere?  

Any insight would be much appreciated.