SplitPane dividers won't move

When running the code below I can't seem to move the dividers at all. I've tried without the HBox also.
Any help would be appreciated. I looked at the list of bugs and didn't seem to find a bug matching.


import java.util.List;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.SplitPane;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class OrganizingUIWithSplitViews extends Application {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Application.launch(OrganizingUIWithSplitViews.class, args);
    }
    
    @Override
    public void start(Stage primaryStage) {
        Group root = new Group();
        Scene scene = new Scene(root, 300, 250, Color.WHITE);
        SplitPane splitPane = new SplitPane();
        splitPane.setPrefSize(400, 400);
        
        List<Node> items = splitPane.getItems();
        items.add(new Button("Left"));
        items.add(new Button("Center"));
        items.add(new Button("Right"));
        

        HBox hbox = new HBox();
        hbox.getChildren().add(splitPane);
        root.getChildren().add(hbox);
        primaryStage.setScene(scene);
        primaryStage.setVisible(true);
    }
}