ADDITIONAL SYSTEM INFORMATION :
Encountered on Windows 10, using OpenJDK 11.0.10.9 with JavaFX 17.0.0.1

A DESCRIPTION OF THE PROBLEM :
When a Menu is embedded in a JFXPanel, clicking on it does not hide it. Instead, it sometimes blink as if closing then immediately reopening.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Executing the provided code will open a window. Clicking any of the menus will open it, clicking again the same menu will not close it.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The menu should be closed. It works correctly when using pure JavaFX (available by replacing the call to useJFXPanel with the one to usePrimaryStage).
ACTUAL -
The menu stays open, and sometimes blinks briefly, as if closed and reopened right after.

---------- BEGIN SOURCE ----------
package testjavafx;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.Pane;
import javafx.scene.layout.Region;
import javafx.stage.Stage;

public class TestMenuJavaFX extends Application {

private static final String TITLE = "test menu JavaFX";


@Override
public void start(Stage primaryStage) {
MenuBar menuBar = new MenuBar(
new Menu("Menu 1", null,
new MenuItem("Menu item 1-1"),
new MenuItem("Menu item 1-2")),
new Menu("Menu 2", null,
new MenuItem("Menu item 2-1"),
new MenuItem("Menu item 2-2")),
new Menu("Menu 3", null,
new MenuItem("Menu item 3-1"),
new MenuItem("Menu item 3-1")));
menuBar.setPrefWidth(300);
Region root = new Pane(menuBar);
root.setPrefSize(300, 185);
useJFXPanel(root);
//usePrimaryStage(primaryStage, root);
}

private static void useJFXPanel(Region root) {
JFXPanel jfxPanel = new JFXPanel();
jfxPanel.setScene(new Scene(root));
SwingUtilities.invokeLater(() -> {
JFrame jFrame = new JFrame(TITLE);
jFrame.setSize((int) root.getWidth(), (int) root.getHeight());
jFrame.add(jfxPanel);
jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jFrame.setLocationRelativeTo(null);
jFrame.setVisible(true);
});
}

private static void usePrimaryStage(Stage primaryStage, Parent root) {
primaryStage.setScene(new Scene(root));
primaryStage.show();
}

public static void main(String[] args) {
launch(TestMenuJavaFX.class, args);
}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Adding this block to the method start before calling useJFXPanel will apparently fix the issue:

menuBar.getMenus().forEach(menu -> {
menu.addEventHandler(Menu.ON_HIDING, e -> {
Platform.runLater(menu::hide);
});
});

FREQUENCY : always