I was trying to use a Layer in such a way that moving or removing the Layer would reveal the formerly obscured part of the underlying Layer. But it didn't work in that way, and I've concluded that it is not intended to work that way. In the examples, the entire display is blanked and re-drawn for every invocation of Scene.draw(), and so there's no need to preserve the underlying pixel values. Can you verify that this conclusion is correct?
Your conclusion is correct.