ATP seems to be using Promise Date not Schedule Ship Date on Internal Sales Orders, giving incorrect

We upgraded to R12.1.3 this year, and have been having some issues with ATP dates being inaccurate for some items (showing available same day when they should not be).  Today, we finally figured out that if we have an internal sales order with a promise date into the future but a scheduled ship date for current date, and demand for items on the internal sales order exceeds current QOH, any new sales orders can take the quantity on hand without regard to the internal sales order that is scheduled.  We believe that ATP is using the promise date or request