I have a child screen section (e.g. BuyOrderItem) and want to feed an input parameter for a dropdown on that screen section with a value from parent entity screen section (column BuyOrder.refSupplierId). This doesn’t work and the dropdown input parameter value isn’t filled and the dropdown isn’t filtered by that value (fails to load).
I found out it’s possible to reference a parent in a dropdown by a name of a relation from it. Actually the name of a relation from a parent is usually a name of a child (detail) entity in a master-detail screen. So in our case I had to write ‘BuyOrderItem.refSupplierId’ to the dropdown parameter mapping. This actually takes the value from parent (BuyOrder’s refSupplierid) which is very confusing, but work well at the end.
Great hint !
Actually this is what I need right now. I hope, that behavior not change in future releases 
You saved me a lot of time.
Jiri