Running the following code make the Label to endlessly increasing its width. The horizontal-scroll-bar in +- 2 seconds or so since the initial width of the Label is smaller than the ScrollView. Then the scroll-bar handle starts to shrink and extend the space where you can scroll.
{code}
javafx.stage.Stage {
    scene: javafx.scene.Scene {
        content: javafx.scene.control.ScrollView {
            node: javafx.scene.control.Label {
                textWrap: true
                text: "A"
            }
        }
    }
}
{code}