To reproduce:
1) unzip ScrollViewTest6.zip
2) open with NB and setup the SDK jar path
3) run
4) resize the displayed window
     -> change listener attached to ScrollPane.layoutBounds() is invoked
           -> viewportBounds is always null
     -> change listener attached to ScrollPane.viewportBounds() is never invoked

I use the following SDK build:

$ cat sdk/timestamp
Product: javafx-2.0beta
Platform: macosx-universal
Build-Number: 202
Build-ID: 2011-07-12_03-02-48$