IR Before GR

Hello

I Have one scheduling Agreeemnt #XYZ.... for this i have maintained the Inforecord also.

This Scheduling agreement is IR (is not GR based Invoice.)

when we post the Invoice then system ask me the Quantity and Value in Invoice, i had entered the quantity and value correctly,

but when i make the GR for the same quantity, the the price updated in purchase order history table is wrongly, it takes the price from material master.why? is it correct

plz guide me why it is wrong?

sapman