JavaFX TreeTableView bug in Java 9

TreeTableViewTestApp.java

import java.util.Random;
import javafx.application.Application;
import javafx.beans.property.ReadOnlyIntegerWrapper;
import javafx.beans.property.ReadOnlyStringWrapper;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableView;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class TreeTableViewTestApp extends Application
{
    private static final Color CATEGORY_COLOR = new Color(1.0, 1.0, 0.7, 1.0);
    private static final Color TOPIC_COLOR = new Color(0.7, 1.0, 1.0, 1.0);
    private static final Random random = new Random();

    private static Node createCircle(Color color) {
        final Circle circle = new Circle(4.0);
        circle.setFill(color);
        circle.setStroke(Color.BLACK);
        circle.setStrokeWidth(0.5);
        return circle;
    }

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        final TreeItem<String> rootItem = new TreeItem<>("Root");
        rootItem.setGraphic(createCircle(new Color(1.0, 0.7, 1.0, 1.0)));
        for (int i = 0; i < 5; i++) {
            final TreeItem<String> categoryItem = new TreeItem<>("Category " + i);
            categoryItem.setGraphic(createCircle(CATEGORY_COLOR));
            rootItem.getChildren().add(categoryItem);
            for (int j = 0; j < 5; j++) {
                final TreeItem<String> topicItem = new TreeItem<>("Topic " + (i * 10 + j));
                topicItem.setGraphic(createCircle(TOPIC_COLOR));
                categoryItem.getChildren().add(topicItem);
            }
        }
        final TreeTableView<String> treeTableView = new TreeTableView<>(rootItem);

        final TreeTableColumn<String, String> column1 = new TreeTableColumn<>();
        column1.setText("Name");
        column1.setPrefWidth(300.0);
        column1.setCellValueFactory(features -> new ReadOnlyStringWrapper(features.getValue().getValue()));

        final TreeTableColumn<String, Number> column2 = new TreeTableColumn<>();
        column2.setText("Size");
        column2.setPrefWidth(100.0);
        column2.setCellValueFactory(features -> new ReadOnlyIntegerWrapper(random.nextInt(1000)));

        treeTableView.getColumns().addAll(column1, column2);

        final BorderPane borderPane = new BorderPane(treeTableView);
        final Scene scene = new Scene(borderPane);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}