After accessing a Menu by its mnemonic, pressing the left or the right arrow key will result in a NullPointerException. The previous issue (linked via clone) was closed as could not reproduce. However, I just discovered this bug myself and can reliably reproduce it on Windows 8.1 using Java SE 7u45 (64 bit), using the same snippet as before. Only my stack trace is slightly different (updated below).

Code:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class JavaFXApplication extends Application {

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

    @Override
    public void start(Stage primaryStage) {

        StackPane root = new StackPane();

        MenuBar menuBar = new MenuBar();
        Menu menuFile = new Menu("_File");
        MenuItem menuItem1 = new MenuItem("Foo");

        menuFile.getItems().add(menuItem1);
        menuBar.getMenus().add(menuFile);

        root.getChildren().add(menuBar);

        primaryStage.setScene(new Scene(root, 300, 250));
        primaryStage.show();
    }
}

Exception:
java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.MenuBarSkin.isMenuEmpty(MenuBarSkin.java:728)
at com.sun.javafx.scene.control.skin.MenuBarSkin.showNextMenu(MenuBarSkin.java:781)
at com.sun.javafx.scene.control.skin.MenuBarSkin.access$600(MenuBarSkin.java:81)
at com.sun.javafx.scene.control.skin.MenuBarSkin$4.handle(MenuBarSkin.java:221)
at com.sun.javafx.scene.control.skin.MenuBarSkin$4.handle(MenuBarSkin.java:194)
at com.sun.javafx.scene.control.WeakEventHandler.handle(WeakEventHandler.java:62)
at com.sun.javafx.event.CompositeEventHandler.dispatchCapturingEvent(CompositeEventHandler.java:78)
at com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:202)
at com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:159)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchCapturingEvent(CompositeEventDispatcher.java:22)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:31)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3496)
at javafx.scene.Scene$KeyHandler.access$2300(Scene.java:3455)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:1904)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2253)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:136)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:100)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:163)
at com.sun.glass.ui.View.handleKeyEvent(View.java:520)
at com.sun.glass.ui.View.notifyKey(View.java:953)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:17)
at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:67)
at java.lang.Thread.run(Thread.java:744)