Drawing items on another item in Omnigraffle

Question

I have a rectangle on canvas, which has no stroke, no shadow, soft color fill, residing half page and acting as grouping background. When I draw new items on that "background" the shadow for new item is not drawn. As long as I move away my item to canvas I can see shadow.

How can I draw an item on other item and have the shadow visible for the top item?

Answer 1

In Omnigraffle 4 there is a button in the Shadow inspector that switches whether shadows for an object are shown on other objects or the background:

Answer 2

You can also place the objects in different layers.