为什么javafx.concurrent.Task在尝试将子项添加到javafx.scene.layout.Pane时停止？

Question

喜欢主题：当我尝试将子项添加到Pane时，为什么Task会停止？如何在不离开任务的情况下解决这个问题？下面的工作示例：

import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Ellipse;
import javafx.stage.Stage;

public class TEST extends Application {

    private Pane displayPane;

    public Parent createContent() {

        /* layout */
        BorderPane layout = new BorderPane();

        /* layout -> center */
        displayPane = new Pane();
        displayPane.setMinSize(200, 200);
        displayPane.setMaxSize(200, 200);

        /* return layout */
        layout.setCenter(displayPane);

        return layout;
    }

    @Override
    public void start(Stage stage) throws Exception {
        stage.setScene(new Scene(createContent()));
        stage.show();

        startTask();
    }

    public void startTask() {
        Task task = new Task<Void>() {
            @Override
            public Void call() {

                // This works fine.
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }


                for (int i = 0; i < 5; i++) {
                    System.out.println("Iteration no.: " + i);
                    Ellipse ellipse = new Ellipse(100, 100, 10, 10);
                    ellipse.setFill(Color.BLACK);

                    // Here task stops on iteration np.: 0.
                    displayPane.getChildren().add(ellipse);
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                    displayPane.getChildren().remove(displayPane.getChildren().size() - 1);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                }
                return null;
            }
        };
        new Thread(task).start();
    }
}