Cost roll up of Parent Item that has component (with average cost)

Summary

Cost roll up of Parent Item that has component (with average cost)- Is this possible?

Content

Cost roll up of Parent Item that has component (with average cost):

We have a FG item that is using standard costing. This FG item has a component that is under Avg costing. When we rollup cost for parent item we get an error stating cost missing for component. Want to know if this is standard functionality (requiring all components under parent to be using standard cost) or is it a bug?