ATP is not considering the onhand availablity while booking the sales order line

Hello All,

Lets consider one scenario\

I have 100 quantity in one sub inventory and the sub inventory have allow ATP, Allow reservation check box been checked.The quantity having onhand =100, ATR=100, ATT=100

We have two sales order line for 50 each against the same item. But when we go and see the second sales order line's ATP details, system showing 100 quantity.Actually it should give 50

Awaiting your reply,

Vijay