Im using the Atlantfx for javafx layout. I’m using a Popover but if it was once visible, the application keeps running in the background after closing.

Minimal example code:

import atlantafx.base.theme.NordLight;
import atlantafx.base.controls.Popover;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Slider;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class Popup extends Application {
    public void start(Stage stage)
    {
        Application.setUserAgentStylesheet(new NordLight().getUserAgentStylesheet());

        Button button = new Button("show");

        BorderPane pane = new BorderPane();
        pane.setCenter(button);

        Slider slider = new Slider();
        slider.setMinWidth(80);
        slider.setMinHeight(40);

        Popover popover = new Popover(slider);
        popover.setHeaderAlwaysVisible(false);
        popover.setArrowLocation(Popover.ArrowLocation.LEFT_TOP);

        button.setOnAction(actionEvent -> {
            if (!popover.isShowing())
                popover.show(button);
            else 
                popover.hide();
        });

        Scene scene = new Scene(pane, 200, 200);
        stage.setScene(scene);

        stage.show();
    }

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

If the Popover was once shown, there is an additional Thread started, that keeps running after closing the application. Am I’m doing something wrong, or is it a bug in Atlantafx?