If a Region is set as a Scene root, its layout bounds are calculated only once (during the first layout pass). Any further changes to its children have no effect on its layout bounds.
Comments
Currently, there is no use-case for this. Might cause issues with backwards compatibility.
11-09-2013
To reproduce run the attached PaneAsRootTest and observe the number of layout bounds change notifications in the output console. If the Pane is wrapped in a Group (see the wrap method), the Pane layout bounds are correctly kept up to date.