See attached movie and attached code:

Problem: if orientation has changed from horizontal to vertical, arrows' orientation was not changed.

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Orientation;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ScrollBar;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class ScrollBarProblem extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        Button someButton = new Button("SomeButton");
        final ScrollBar slider = new ScrollBar();

        someButton.setOnAction(new EventHandler<ActionEvent>() {

            @Override
            public void handle(ActionEvent t) {
                slider.setOrientation(Orientation.VERTICAL);
            }
        });

        VBox pane = new VBox();
        pane.getChildren().addAll(slider, someButton);
        Scene scene = new Scene(pane, 200, 200);
        stage.setScene(scene);
        stage.show();
    }
}