Start SB.
--> the top AnchorPane is already selected, one sees the blue selection ring on content
Take "Menu > Edit > Select All"
--> on content the blue selection ring goes away, replaced by the parent ring (thick orange one). I'm not sure this is correct.
Now you see in "Menu > File" the "Duplicate" action became enabled; if you take it it does nothing.

If top element is Border or Stack pane it does all the same.

As soon as one or more item are dropped on content Select All behaves as expected.