Item Revision defaulted on Requisition is not correct based revision effectivity dates

Hi All,

Release 12.1.3

Have an Item with with following revisions
Rev A effective through 10/4/12
Rev B effective 10/5 through 10/14
Rev C effective date 10/15
We have planned order generated in MRP with implementation date 10/7 and 10/18. When the requisitions are released the revisio on the requisition defaults to A which the the current effective revision. Expected result is for Rev B to default if implementation  date is 10/7 and for Rev C to default if date is 10/18.
We need clarification on standard functionality.
MRP: Purchase by Revision is set to Yes
Item is NOT revision controlled

Thanks.