AX 2009 ATP not including planned orders even though the check box has been set to on

We are trying to use the ATP function and have the “include planned orders” check box set to on but the ATP function does not show the planned purchase orders as receipts for the ATP calculation, it will only work with firmed POs even though the item coverage is set for POs and using requirements as the coverage code. Is this a bug in the code or is there some other setting in AR parameters that I am missing?

Thanks!

Melissa