order/PR price integration process flawed?

1) Maintenance planner creates PM work order with non-stock purchase, price/vendor unknown
2) PR is generated. Buyer proceeds to source the part, create info record, update price/vendor
3) Planner changes work order schedule. This date change automatically updates the PR delivery date, and furthermore the blank/null price on the PM work order purchasing screen OVERWRITES THE PRICE SET BY THE BUYER. (It's too bad the PR price does not flow back into the component purchasing screen)

Surely this can't be the standard process put out by SAP. What am I missing here? How can the planner change the work order scheduling without erasing the PR price?

Thanks, Vlad