AutoCreate Purchase Order cannot approve

Hi a newbies in Purchasing need assistance for this

I have created an autocreate purchase order with a amount of less than 1000 when i click the <Approve> button my expectation is that the Approval status column should be Approved since i have the approval group for less than 5000.

Also i have created a standard purchase order with same amount as above upon clicking the approve button the approval status column is Approved.

Why if i used the AutoCrease Purchase Order its not approved it goes to my supervisor even though the PO amount is within my apporval capacity ?

Thanks