PO CONFIRMATION CONTROL KEY SEQUENCE

I configured a confirmation control key withthe below sequence:

1. For AB,(Order Acknowledgement) and,

2.For LA (Inbound Delivery)

When I use this confirmation control key in the Purchase Order, system is allowing me to create the Inbound delivery with AB as well. How to restrict this or Are there any SAP Notes available to correct this behaviour? Kindly help.It is very urgent. Thanks.

SasiKanth J