Expanding nodes in a TreeView I am seeing these:
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
        at com.sun.javafx.scene.control.accessible.AccessibleListItem.isSelected(Unknown Source)
        at com.sun.glass.ui.accessible.win.WinAccessibleSelectionItemProvider.getIsSelected(Unknown Source)
        at com.sun.glass.ui.accessible.win.WinAccessibleBaseProvider._fireEvent(Native Method)
        at com.sun.glass.ui.accessible.win.WinAccessibleBaseProvider.fireEvent(Unknown Source)
        at com.sun.javafx.tk.quantum.WindowStage.accessibleFireEvent(Unknown Source)
        at com.sun.javafx.accessible.AccessibleNode.fireEvent(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl.fireEvent(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl$1.changed(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl$1.changed(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
        at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(Unknown Source)
        at javafx.scene.Node$FocusedProperty.notifyListeners(Unknown Source)
        at javafx.scene.Node.setFocused(Unknown Source)
        at javafx.scene.control.TreeCell.updateFocus(Unknown Source)
        at javafx.scene.control.TreeCell.indexChanged(Unknown Source)
        at javafx.scene.control.IndexedCell.updateIndex(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.setCellIndex(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.addTrailingCells(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Scene.doLayoutPass(Unknown Source)
        at javafx.scene.Scene$ScenePulseListener.pulse(Unknown Source)
        at com.sun.javafx.tk.Toolkit.firePulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(Unknown Source)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.access$300(Unknown Source)
        at com.sun.glass.ui.win.WinApplication$3$1.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Exception in thread "JavaFX Application Thread" java.lang.UnsupportedOperationException
        at com.sun.javafx.scene.control.accessible.AccessibleListItem.getSelectionContainer(Unknown Source)
        at com.sun.glass.ui.accessible.win.WinAccessibleSelectionItemProvider.getSelectionContainer(Unknown Source)
        at com.sun.glass.ui.accessible.win.WinAccessibleBaseProvider._fireEvent(Native Method)
        at com.sun.glass.ui.accessible.win.WinAccessibleBaseProvider.fireEvent(Unknown Source)
        at com.sun.javafx.tk.quantum.WindowStage.accessibleFireEvent(Unknown Source)
        at com.sun.javafx.accessible.AccessibleNode.fireEvent(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl.fireEvent(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl$1.changed(Unknown Source)
        at com.sun.javafx.scene.control.accessible.AccessibleControl$1.changed(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
        at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(Unknown Source)
        at javafx.scene.Node$FocusedProperty.notifyListeners(Unknown Source)
        at javafx.scene.Node.setFocused(Unknown Source)
        at javafx.scene.control.TreeCell.updateFocus(Unknown Source)
        at javafx.scene.control.TreeCell.indexChanged(Unknown Source)
        at javafx.scene.control.IndexedCell.updateIndex(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.setCellIndex(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.addTrailingCells(Unknown Source)
        at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Parent.layout(Unknown Source)
        at javafx.scene.Scene.doLayoutPass(Unknown Source)
        at javafx.scene.Scene$ScenePulseListener.pulse(Unknown Source)
        at com.sun.javafx.tk.Toolkit.firePulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(Unknown Source)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.access$300(Unknown Source)
        at com.sun.glass.ui.win.WinApplication$3$1.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

This does not happen with JavaFX 8b106.