Changes in production order is becoming MRP relevant

Hello,

I am facing an issue request for suitable input on this,

Scenario :- Sales order based MRP is run MD50, the generated planned order is converted to production order.

                   Then user is increasing the procurement component quantity in production order and again running MRP.

                   System is then increasing the quantity of PR against this sales order and that particular component.

                   What could be the reason for this since changes in production order is not relevant to MRP.

Regards,

Sandip Shrivas