JDK-8371781 Popup for ComboBox, Menu, and Tooltip is not shown sometimes in JavaFX

[PavelTurk]

Hello, everyone

I opened JDK-8371781, but it was closed as “cannot reproduce.” Since the issue is very serious, I am providing a complete example along with a GIF file showing how to reproduce it. I want to emphasize that the problem does not occur consistently, but intermittently. Sometimes you need to perform the same action 30–40 times to reproduce it.

GIF (about 15 seconds) - https://ibb.co/n8Y42bNy

Test code:

public class Test1 extends Application {

     private final Label label = new Label("Miracles don’t happen.");

     @Override
     public void start(Stage stage) {
         MenuItem item = new MenuItem("Click me!");
         item.setOnAction(e -> {
             label.setText("It’s a miracle!");
         });
         Menu menu = new Menu("Menu");
         menu.getItems().add(item);
         MenuBar bar = new MenuBar(menu);

         var stackPane = new StackPane(label);
         VBox.setVgrow(stackPane, Priority.ALWAYS);
         label.setStyle("-fx-font-size: 30");
         VBox root = new VBox(bar, stackPane);

         Scene scene = new Scene(root, 400, 400);
         stage.setScene(scene);
         stage.setTitle("JDK-8371781");
         stage.show();
     }

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

Best regards, Pavel