The second box should not have attached backing store.

(GraphicsLayer
  (anchor 0.00 0.00)
  (bounds 785.00 2024.00)
  (backingStoreAttached 1)
  (children 1
    (GraphicsLayer
      (bounds 785.00 2024.00)
      (contentsOpaque 1)
      (backingStoreAttached 1)
      (children 2
        (GraphicsLayer
          (position 20.00 20.00)
          (bounds 100.00 100.00)
          (contentsOpaque 1)
          (drawsContent 1)
          (backingStoreAttached 1)
        )
        (GraphicsLayer
          (position 20.00 1500.00)
          (bounds 100.00 100.00)
          (contentsOpaque 1)
          (drawsContent 1)
          (backingStoreAttached 0)
        )
      )
    )
  )
)
visible boxhidden box