Error in call out order

Dear Sir,

I was created value (WK) based contract with Target value 10000 INR. Below material, Quantity and value we had mention in value based contract.

PO line     Material       Quantity      Net price

10              1000123          1                100

Through that Value based contract I am creating call out order (PO) with quantity 5. At that time system giving me error that target quantity 4 is exceeds.

As per my understanding if it is value contract while creating RO against contract it should only control value not the quantity but here why system controlling quantity.?

Thanks,

Bhaumik