See attached video. (You will see problem with bidirectional binding. Problem with unidirectional binding is the same.)

I have some problems with bidirectional and unidirectional bindings which should set preferable viewport width and height. Sometimes setting work, sometimes doesn't work at all. Also it stops working after successful setting by any binding (for example, set value by bidirectional binding and it will be attached, try again and you will have no result). But you can see on video, that listeners see properties changing.

In my example ScrollPane is in Pane. Pane is in HBox which is the root element of the scene.