I have noticed that Path class has method that returns non-public class:
protected com.sun.javafx.css.StyleableProperty getStyleablePropertyForFillProperty()
* Stylesheet Handling * *

See http://jfx.sfbay.sun.com/hudson/view/2.1/job/2.1/61/label=windows-i586-14/artifact/artifacts/public/sdk/docs/api/javafx/scene/shape/Path.html

There can be more such cases