Drop Shipping & Purchase Order with product bundle

Hi , we using ERPNext with a drop shipping workflow SO => PO => PI => SI.

This works fine for all items except a product bundle.
By adding a PO to a SO we have the bundle product in the item list. Picking the elements of bundle in the menu, all single items of the bundle will be listed in the PO but not marked as “shipped by supplier”.
A detour with a Material Request in between results the same.

Any idea how we can order the single items of a product bundle marked for drop shipping?