Javafx TreeItem/TreeView UI crashes when collapsing the expanded node. Any help would be appreciated

Question

Step to produce the bug

1. Run this code
2. Expand the root node, if not expanded
3. Collapse the root node
4. More folders (like subfolders) will appear at the end of the window

---

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TreeCell;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
import javafx.util.Callback;

public class Main extends Application {

    Pane box;
    TreeView<String> treeView;

    @Override
    public void start(Stage stage) {

        TreeItem<String> root = new TreeItem<>("Root");
        traverse("a folder path", root);
        root.setExpanded(true);

        treeView = new TreeView<String>(root);
        treeView.setShowRoot(true);
        treeView.setEditable(true);
        treeView.setPrefSize(500, 800);

        treeView.setCellFactory(new Callback<TreeView<String>, TreeCell<String>>() {
            @Override
            public TreeCell<String> call(TreeView<String> paramP) {
                return new TreeCell<String>() {
                    @Override
                    protected void updateItem(String paramT, boolean paramBoolean) {
                        super.updateItem(paramT, paramBoolean);
                        if (!isEmpty()) {
                            setGraphic(new Label(paramT, (Node) importImage("image path")));
                            setOnMouseClicked(new EventHandler<MouseEvent>() {
                                @Override
                                public void handle(MouseEvent event) {

                                    P.print(paramT);
                                    P.print(treeView.getChildrenUnmodifiable().size());
                                }
                            });
                        }
                    }
                };
            }
        });

        box = new Pane();
        box.getChildren().add(treeView);
        box.setPrefSize(500, 800);

        Scene scene = new Scene(box, 500, 800);

        stage.setTitle("Tree View Sample");
        stage.setScene(scene);
        stage.show();
    }

    public void traverse(String path, TreeItem<String> root) {
        File file = new File(path);

        if (!file.isDirectory() || !Files.isReadable(Paths.get(path)))
            return;
        Arrays.asList(file.listFiles()).forEach(e -> {
            TreeItem<String> temp = new TreeItem<>(e.getName());
            root.getChildren().add(temp);
            traverse(e.getPath(), temp);
        });

    }

    public static ImageView importImage(String path) {
        ImageView image = new ImageView(new Image(path));
        image.setPreserveRatio(true);
        image.setFitHeight(20);

        return image;
    }

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

}