The attached NetBeans project runs an FX app where there's a single button.
First click builds a MenuBar instance and add it to the scene.
Second click removes it from the scene.
Third click removes it again and this time we get a stack, extract below.
Note that with FX 2.2 promoted b12 it was doing fine.

Caused by: java.lang.NullPointerException
    at com.sun.javafx.scene.control.skin.MenuBarSkin$10.changed(MenuBarSkin.java:313)
    at com.sun.javafx.scene.control.skin.MenuBarSkin$10.changed(MenuBarSkin.java:308)
    at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:196)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:100)
    at javafx.beans.property.ReadOnlyObjectWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyObjectWrapper.java:195)
    at javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:161)
    at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:130)
    at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:163)
    at javafx.scene.Node.setScene(Node.java:673)
    at javafx.scene.Parent$1.onChanged(Parent.java:425)
    at com.sun.javafx.collections.VetoableObservableList.callObservers(VetoableObservableList.java:83)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:154)
    at com.sun.javafx.collections.VetoableObservableList.add(VetoableObservableList.java:167)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:144)
    at glop.MainWindowController.onAdd(MainWindowController.java:40)
    ... 46 more