Hello Zaneta,
If i am understanding your query corrrectly, SAP uses this logic for project stock valuation. On what basis this is being used, i am not having any idea.
If your production order has a planned costing variant, and a planned cost is being calculated, system uses this value to valuate the production order even if there is a released standard price for the material master.
I am also facing this issue. So i used the user exit with in the second strategy to force the standard price of material master for production order goods receipt valuation.
thanks
Hari