Further to my earlier bug (RT-37362 ), I tried making my Swing/JavaFX application into a JavaFX application to get around the menubar issue. However, I have found a new problem: If you have a JavaFX menu with a MenuBar that has useSystemMenuBar set to true, and you have a Swing menu having called System.setProperty("apple.laf.useScreenMenuBar", "true"), then when you switch to the JavaFX window then the Swing window, the menus for *both* windows appear in the menu bar. Steps to reproduce:

// A scene with a JavaFX menu that goes in the system menu bar:
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.VBox;


public class MenuScene extends Scene
{
    public MenuScene()
    {
        super(new VBox());
        MenuBar m = new MenuBar();
        Menu menu = new Menu("JavaFX");
        menu.getItems().add(new MenuItem("My item"));
        m.getMenus().add(menu);
        m.setUseSystemMenuBar(true);
        
        ((VBox)getRoot()).getChildren().addAll(m, new Label("Content"));
    }
}


// An application that makes a JavaFX window with a system menu bar and a Swing window with a system menu bar:
import javafx.application.Application;
import javafx.stage.Stage;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.SwingUtilities;


public class TestMenuMixing extends Application {

    @Override
    public void start(Stage stage) throws Exception
    {
        // Primary has menu:
        stage.setScene(new MenuScene());
        stage.show();
        
        // Also show a Swing Window with menu:
        SwingUtilities.invokeLater(() -> {
            System.setProperty("apple.laf.useScreenMenuBar", "true");
            JFrame window = new JFrame();
            JMenuBar menuBar = new JMenuBar();
            menuBar.add(new JMenu("Swing"));
            window.setJMenuBar(menuBar);
            window.setVisible(true);
        });
    }
}

Run that code, and switch to the Swing window. It only shows "Swing" in the menu bar. Switch to the JavaFX window, and it shows "Swing" *and* "JavaFX" (it should only show "JavaFX").