Hi,
The process should be different from what you describe. First, you create a contract specifying the commitment plan. This will create an earmarked fund (reservation); it will happen immediately if you flag 'generate CP item'. Then, your logistic chain will refer to this reservation.
Regards,
Eli
P.S. PRs should be posted statistically, in your case, as indeed, it will create double-consumption of budget.
P.P.S You can consult this link for more info Commitment Plan - Defense MILSTRIP Purchasing - SAP Library