JavaFX : Menu on a MenuBar disappears instantly on click?

I am trying out a book example on a simple MenuBar.
The menu bar shows a single File menu, which when clicked should show the individual Open, Close, Save menu items. But as soon as I click on the File menu, those menu items appear in a flash and then disappear in like 1 second. What is going on? Please advise.

Code:

import javafx.application.*;
import javafx.scene.*;
import javafx.stage.*;
import javafx.scene.layout.*;
import javafx.scene.control.*;
import javafx.event.*;
import javafx.geometry.*;
   
public class MenuDemo extends Application {
   
    Label response;
   
    public static void main(String[] args) {
        launch(args);
    }
   
    @Override
    public void start(Stage pStage) {
        pStage.setTitle("Menu Bar Example");
        BorderPane rootNode = new BorderPane();
        Scene myScene = new Scene(rootNode, 300, 300);
        pStage.setScene(myScene);
        response = new Label("fooo");
       
        MenuBar mb = new MenuBar();
       
        Menu fileMenu = new Menu("File");
        MenuItem open = new MenuItem("Open");
        MenuItem close = new MenuItem("Close");
        MenuItem save = new MenuItem("Save");
        MenuItem exit = new MenuItem("Exit");
        //add the items to the menu
        fileMenu.getItems().addAll(open, close, save, exit);
       
        //add the menu to the menu bar
        mb.getMenus().add(fileMenu);
       
       //a handler to display the menuItem clicked on response label
        EventHandler<ActionEvent> menuCall = new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent e) {
                String itemSelected = ((MenuItem)e.getTarget()).getText();
                response.setText("The selected item is: " + itemSelected);
            }
        };
       
        open.setOnAction(menuCall);
        close.setOnAction(menuCall);
        save.setOnAction(menuCall);
        exit.setOnAction(menuCall);
       
        rootNode.setTop(mb);
        rootNode.setCenter(response);
       
        pStage.show();
    }   
   
}

 

It was a problem with the IDE BlueJ..it works when running from the command line

 

it works with netBeans IDE.