Hi Patrick
This is happening because the parent material is using a planning strategy of preplanning without final assembly. In this case, system will generate unconvertible VP planned orders for the parent material.
You can control the behavior of the components using the field "individual/collective" of the material master tab MRP4. If you choose the value 2 for the component, MRP will treat it as a standard component and generate purchase requisitions.
BR
Caetano