filechooser showSaveDialog() not display title

[taihuapp]

Here is the sample code:

package sample;

import javafx.application.Application;
import javafx.stage.FileChooser;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) {
        FileChooser fileChooser = new FileChooser();
        fileChooser.setTitle("Saving file ...");
        fileChooser.showSaveDialog(primaryStage);
    }

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

When the above code was running with openjfx library 15.0.1 or 11.0.2, the title "Saving file ..." is not shown. It works properly with Java 8, though.

I'm running Ubuntu 20.04.