Ticket raise by project user: 

Have created a material component under an activity and PR was created for 10 items immediately. I also created a PO for 10 items.
 
The issue is that the users are able to go back in the Projects and reduce the material quantity to 5 for example. So after saving the quantity automatically changes in PR. But the PO is still present for 10 items.  Thus giving an discrepancy in the PR and PO.
 
Is there any configuration missing on my part?

Resolution:

Check SAP Note 497090 - "Blocking Purchase Orders/requisitions/commitments from networks":

"The creation of a material entry in the network is seen as a part of the planning process and therefore must not be blocked.

Precise meaning:

RMBA = the manual creation of a purchase requisition for material from materials management.

and

RMBE = The manual creation of a purchase order material from materials management.

These business transactions are definitely not checked when a material entry is created in the network, even if a purchase requisition is also generated. Business transactions RMBA and RMBE are also not checked when a purchase order is created from a purchase requisition which is generated in this way.
Therefore, it is not possible to prevent the creation of a material entry in the network and the corresponding purchase requisition and the subsequent purchase order explicitly using a user-defined status in the network/ network activity.

This also means that it is not possible to prevent the generation of the respective commitment.

However, the creation of the purchase order can be checked via a corresponding release procedure in the materials management.

In contrast to this:

The generic materials management transactions check these business transactions for purchase requisitions created directly in materials management, and purchase orders or purchase orders that result from purchase requisitions created directly in materials management and, if necessary, send a corresponding error message."

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