Restrictions in PO

Hi Experts

when ever i create Po, ERS and invoice receipt tick is automatically flowing the PO.

I checked in vendor master master autoERS has been set with somany vendor master.

But if i use few vendor master , ERS and invoice set is flowing automatically into PO.

Can some body tel me What are the criteria which will allow ERS and Ivoice set automatically into PO?

And

How to stop these automatic set mark in the PO(While creating PO).

Thanks