Exception in ActiproSoftware.Docking.Wpf351.dll

I get a null reference exception in ActiproSoftware.Docking.Wpf351.dll when I use IsOpen binding and the layout serializer.

My ToolWindow is defined as:

<docking:ToolWindow Name="twStateCountry" Title="State &amp; County" Focusable="False" IsOpen="{Binding StateCountryIsOpen}">
</docking:ToolWindow>

StateCountryIsOpen is defined as:

public bool StateCountryIsOpen
{
get
{
return _stateCountryIsOpen;
}

set
{
if (_stateCountryIsOpen != value)
{
_stateCountryIsOpen = value;
OnPropertyChanged("StateCountryIsOpen");
}
}
}

Layout serialization is done as:

DockSite dockSite = window.FindName("dockSite") as DockSite;

if ((object)dockSite != null)
{
DockSiteLayoutSerializer layoutSerializer = new DockSiteLayoutSerializer();

if ((object)layoutSerializer != null)
layoutSerializer.LoadFromString(xxx.yyy.Admin.Properties.Settings.Default.Layout.OuterXml, dockSite);

If I remove the IsOpen binding, everything works correctly.

Call stack is:

ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(ActiproSoftware.Windows.Controls.Docking.DockingWindow A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, ActiproSoftware.Windows.Controls.Docking.DockingWindowCloseReason A_1 = Other, bool A_2 = false, bool A_3 = false) + 0x43e bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(ActiproSoftware.Windows.Controls.Docking.DockingWindow A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, ActiproSoftware.Windows.Controls.Docking.DockingWindowCloseReason A_1 = Other, bool A_2 = false) + 0x30 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockingWindow.Close() + 0x57 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockingWindow.p(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, System.Windows.DependencyPropertyChangedEventArgs A_1 = {System.Windows.DependencyPropertyChangedEventArgs}) + 0x90 bytes
WindowsBase.dll!System.Windows.DependencyObject.OnPropertyChanged(System.Windows.DependencyPropertyChangedEventArgs e) + 0x4c bytes
PresentationFramework.dll!System.Windows.FrameworkElement.OnPropertyChanged(System.Windows.DependencyPropertyChangedEventArgs e) + 0x50 bytes
WindowsBase.dll!System.Windows.DependencyObject.NotifyPropertyChange(System.Windows.DependencyPropertyChangedEventArgs args) + 0x3c bytes
WindowsBase.dll!System.Windows.DependencyObject.UpdateEffectiveValue(System.Windows.EntryIndex entryIndex = {System.Windows.EntryIndex}, System.Windows.DependencyProperty dp = {System.Windows.DependencyProperty}, System.Windows.PropertyMetadata metadata, System.Windows.EffectiveValueEntry oldEntry, ref System.Windows.EffectiveValueEntry newEntry = {System.Windows.EffectiveValueEntry}, bool coerceWithDeferredReference, bool coerceWithCurrentValue, System.Windows.OperationType operationType) + 0x723 bytes
WindowsBase.dll!System.Windows.DependencyObject.InvalidateProperty(System.Windows.DependencyProperty dp) + 0xad bytes
PresentationFramework.dll!System.Windows.Data.BindingExpressionBase.Invalidate(bool isASubPropertyChange) + 0x62 bytes
PresentationFramework.dll!System.Windows.Data.BindingExpression.TransferValue(object newValue, bool isASubPropertyChange) + 0x1fd bytes
PresentationFramework.dll!System.Windows.Data.BindingExpression.Activate(object item) + 0x194 bytes
PresentationFramework.dll!System.Windows.Data.BindingExpression.OnDataContextChanged(System.Windows.DependencyObject contextElement) + 0x67 bytes
PresentationFramework.dll!System.Windows.Data.BindingExpression.HandlePropertyInvalidation(System.Windows.DependencyObject d = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, System.Windows.DependencyPropertyChangedEventArgs args) + 0xc7 bytes
PresentationFramework.dll!System.Windows.Data.BindingExpressionBase.OnPropertyInvalidation(System.Windows.DependencyObject d, System.Windows.DependencyPropertyChangedEventArgs args) + 0x5f bytes
PresentationFramework.dll!System.Windows.Data.BindingExpression.OnPropertyInvalidation(System.Windows.DependencyObject d, System.Windows.DependencyPropertyChangedEventArgs args) + 0xcc bytes
WindowsBase.dll!System.Windows.DependentList.InvalidateDependents(System.Windows.DependencyObject source = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, System.Windows.DependencyPropertyChangedEventArgs sourceArgs) + 0x89 bytes
WindowsBase.dll!System.Windows.DependencyObject.NotifyPropertyChange(System.Windows.DependencyPropertyChangedEventArgs args) + 0x19b bytes
WindowsBase.dll!System.Windows.DependencyObject.UpdateEffectiveValue(System.Windows.EntryIndex entryIndex = {System.Windows.EntryIndex}, System.Windows.DependencyProperty dp = {System.Windows.DependencyProperty}, System.Windows.PropertyMetadata metadata, System.Windows.EffectiveValueEntry oldEntry, ref System.Windows.EffectiveValueEntry newEntry = {System.Windows.EffectiveValueEntry}, bool coerceWithDeferredReference, bool coerceWithCurrentValue, System.Windows.OperationType operationType) + 0x723 bytes
PresentationFramework.dll!System.Windows.TreeWalkHelper.InvalidateTreeDependentProperty(System.Windows.TreeChangeInfo info, System.Windows.DependencyObject d, ref MS.Internal.FrameworkObject fo, System.Windows.DependencyProperty dp, System.Windows.FrameworkPropertyMetadata fMetadata, System.Windows.Style selfStyle, System.Windows.Style selfThemeStyle, ref System.Windows.ChildRecord childRecord, bool isChildRecordValid, bool hasStyleChanged, bool isSelfInheritanceParent) + 0x10a bytes
PresentationFramework.dll!System.Windows.TreeWalkHelper.InvalidateTreeDependentProperties(System.Windows.TreeChangeInfo info, System.Windows.FrameworkElement fe, System.Windows.FrameworkContentElement fce, System.Windows.Style selfStyle = null, System.Windows.Style selfThemeStyle = {System.Windows.Style}, ref System.Windows.ChildRecord childRecord = {System.Windows.ChildRecord}, bool isChildRecordValid = false, bool hasStyleChanged = false, bool isSelfInheritanceParent = true) + 0x151 bytes
PresentationFramework.dll!System.Windows.FrameworkElement.InvalidateTreeDependentProperties(System.Windows.TreeChangeInfo parentTreeState, bool isSelfInheritanceParent) + 0x188 bytes
PresentationFramework.dll!System.Windows.FrameworkElement.OnAncestorChangedInternal(System.Windows.TreeChangeInfo parentTreeState) + 0x8e bytes
PresentationFramework.dll!System.Windows.TreeWalkHelper.OnAncestorChanged(System.Windows.DependencyObject d, System.Windows.TreeChangeInfo info) + 0x56 bytes
PresentationFramework.dll!System.Windows.DescendentsWalker<System.Windows.TreeChangeInfo>.StartWalk(System.Windows.DependencyObject startNode, bool skipStartNode) + 0x7c bytes
PresentationFramework.dll!MS.Internal.PrePostDescendentsWalker<System.Windows.TreeChangeInfo>.StartWalk(System.Windows.DependencyObject startNode = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, bool skipStartNode = false) + 0x33 bytes
PresentationFramework.dll!System.Windows.TreeWalkHelper.InvalidateOnTreeChange(System.Windows.FrameworkElement fe, System.Windows.FrameworkContentElement fce, System.Windows.DependencyObject parent, bool isAddOperation) + 0x331 bytes
PresentationFramework.dll!System.Windows.FrameworkElement.ChangeLogicalParent(System.Windows.DependencyObject newParent) + 0xa8 bytes
PresentationFramework.dll!System.Windows.FrameworkElement.RemoveLogicalChild(object child) + 0x7e bytes
PresentationFramework.dll!MS.Internal.Controls.InnerItemCollectionView.ClearModelParent(object item) + 0xaa bytes
PresentationFramework.dll!MS.Internal.Controls.InnerItemCollectionView._RemoveAt(int index = 0, int indexR, object item = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x41 bytes
PresentationFramework.dll!MS.Internal.Controls.InnerItemCollectionView.RemoveAt(int index) + 0x4d bytes
PresentationFramework.dll!System.Windows.Controls.ItemCollection.RemoveAt(int removeIndex) + 0x22 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.Track}, System.Windows.DependencyObject A_1 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, bool A_2 = true) + 0x14c bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.Track}, System.Windows.DependencyObject A_1 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x28 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.af(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x47 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.ab(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x68 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.y(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0xcf bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.ap(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x14b bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.z(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0xae bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.aa(System.Windows.DependencyObject A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}) + 0x63 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(ActiproSoftware.Windows.Controls.Docking.DockingWindow A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, ActiproSoftware.Windows.Controls.Docking.DockingWindowCloseReason A_1 = LayoutCleared, bool A_2 = true, bool A_3 = false) + 0x167 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(ActiproSoftware.Windows.Controls.Docking.DockingWindow A_0 = {ActiproSoftware.Windows.Controls.Docking.ToolWindow}, ActiproSoftware.Windows.Controls.Docking.DockingWindowCloseReason A_1 = LayoutCleared, bool A_2 = true) + 0x30 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.b(ActiproSoftware.Windows.Controls.Docking.EventNotifier A_0 = {ActiproSoftware.Windows.Controls.Docking.EventNotifier}) + 0x352 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Serialization.DockSiteLayoutSerializer.a(ActiproSoftware.Windows.Controls.Docking.DockSite A_0 = {FirstAmerican.RubiSoft.UI.DockSiteEx}, ActiproSoftware.Windows.Controls.Docking.Serialization.XmlDockSiteLayout A_1 = {ActiproSoftware.Windows.Controls.Docking.Serialization.XmlDockSiteLayout}) + 0x159 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Serialization.DockSiteLayoutSerializer.ApplyTo(ActiproSoftware.Windows.Controls.Docking.DockSite obj = {FirstAmerican.RubiSoft.UI.DockSiteEx}) + 0x5b bytes
ActiproSoftware.Shared.Wpf351.dll!ActiproSoftware.Windows.Serialization.XmlSerializerBase<ActiproSoftware.Windows.Controls.Docking.DockSite,ActiproSoftware.Windows.Controls.Docking.Serialization.XmlDockSiteLayout>.LoadFromString(string xml = "<DockSiteLayout xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" SerializationFormat=\"ToolWindowsOnly\"><AutoHideHost /><Content xsi:type=\"SplitContainer\" AutoHideSize=\"785,476\" DockedSize=\"785,476\" DocumentSize=\"785,476\" FloatingSize=\"785,476\" Size=\"785,476\" Orientation=\"Horizontal\"><UIElement xsi:type=\"ToolWindowContainer\" AutoHideSize=\"200,446\" DockedSize=\"200,446\" DocumentSize=\"200,446\" FloatingSize=\"200,446\" Size=\"200,446\" /><UIElement xsi:type=\"Workspace\" AutoHideSize=\"785,476\" DockedSize=\"785,476\" DocumentSize=\"785,476\" FloatingSize=\"785,476\" Size=\"785,476\"><Content xsi:type=\"TabbedMdiHost\"><Content xsi:type=\"TabbedMdiContainer\" AutoHideSize=\"200,200\" DockedSize=\"200,200\" DocumentSize=\"200,200\" FloatingSize=\"200,200\" Size=\"200,200\" /></Content></UIElement></Content><ToolWindows><ToolWindow UniqueId=\"035750c0-1bf7-4b73-9865-6d23af1dc5a5\" AutoHideSize=\"200,200\" DockedSize=\"200,200\" DocumentSize=\"200,200\" FloatingSize=\"200,200\" Size=\"200,200\" IsOpen=\"true\" LastState=\"Docked\" Name=\"twStateCountry\" State=\"Docked\" /></ToolWindows></DockSiteLayout>", ActiproSoftware.Windows.Controls.Docking.DockSite obj = {FirstAmerican.RubiSoft.UI.DockSiteEx}) + 0x34 bytes