I added the graphics to the Tab and added around 10 to 11 tabs to tabpane. Please see the attached screen shot for more under standing of the bug.
I have attached the testcase to reproduce the bug.



----- Test Case ------

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Side;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.RadioButton;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.control.Toggle;
import javafx.scene.control.ToggleGroup;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

/**
 *
 * @author ammulu
 */
public class TabWithGraphics extends Application {

    TabPane tabPane = null;
    ChoiceBox cb = new ChoiceBox();
    Color colors[] = {Color.BLUE, Color.RED, Color.GREEN, Color.GOLD};

    @Override
    public void start(Stage stage) throws Exception {
        stage.setTitle("Hello World");
        Group root = new Group();
        Scene scene = new Scene(root, 500, 500);

        // create a TabPane instance
        tabPane = new TabPane();
        tabPane.setLayoutX(20);
        tabPane.setLayoutY(20);
        // create individual tabs
        for (int i = 0; i <10; i++) {
            Tab tab = new Tab();
            // set the label for tab
            tab.setText("Tab # " + (i + 1));
             ImageView imgView = new ImageView();
             Image img = new Image(TabWithGraphics.class.getResourceAsStream("duke.jpg"));
             imgView.setImage(img);
             imgView.setFitHeight(25);
             imgView.setFitWidth(25);
             imgView.setPreserveRatio(true);
             tab.setGraphic(imgView);

            // add the content to tab
            tab.setContent(new Rectangle(400, 400, Color.GREEN));

            // add the tab to TabPane
            tabPane.getTabs().add(tab);
        }

        // create a hbox to hold the radio buttons
        HBox sideLayout = new HBox();
        sideLayout.setSpacing(10);
        
        final ToggleGroup tg = new ToggleGroup();
        
        RadioButton top = new RadioButton("Top");
        top.setSelected(true);
        top.setUserData("Top");
        top.setToggleGroup(tg);
        
        RadioButton bottom = new RadioButton("Bottom");
        bottom.setToggleGroup(tg);
        bottom.setUserData("Bottom");
        
        RadioButton left = new RadioButton("Left");
        left.setToggleGroup(tg);
        left.setUserData("Left");
        
        RadioButton right = new RadioButton("Right");
        right.setToggleGroup(tg);
        right.setUserData("Right");

        sideLayout.getChildren().addAll(top, bottom, left, right);

        // Add change listener to toggleGroup
        tg.selectedToggleProperty().addListener(new ChangeListener<Toggle>() {

            public void changed(ObservableValue<? extends Toggle> observable, Toggle oldValue, Toggle newValue) {
                String selectedValue = tg.getSelectedToggle().getUserData().toString();
                System.out.println(selectedValue);
                if (selectedValue.equals("Top")) {
                    tabPane.setSide(Side.TOP);
                }
                if (selectedValue.equals("Bottom")) {
                    tabPane.setSide(Side.BOTTOM);
                }
                if (selectedValue.equals("Left")) {
                    tabPane.setSide(Side.LEFT);
                }
                if (selectedValue.equals("Right")) {
                    tabPane.setSide(Side.RIGHT);
                }
            }
        });

        root.getChildren().addAll(sideLayout, tabPane);
        stage.setScene(scene);
        stage.setVisible(true);
    }

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


----------------------------