MRP and APO

Hi,

We have a finished product which is planned in APO, so set up as external planning in ECC. The components are planned in APO, we run the MRP with planning mode = 3 and we can see that the planned order created in APO for the FERT is modified in ECC.

Why is this planned order changed in ECC if it is generated by APO and material is not planned in ECC?

Thanks.