ToolWindows state is lost when DataContext is updated

I have a view which has a docksite attached.  When I change my DataContext the ToolWindows states are lost.  How can I retain the state between DataContext updates?  I have the following code which attempts to save the state when the docksite datacontext is changed.  The ToolWindows have the correct sizes however when  I serialize out the state the XML is incorrect and shows the initialized values.

Even if I trap the _dockSite.WindowsClosing += _dockSite_WindowsClosing event and try to serialize out the values are incorrect.  The only time the serialization is correct is when I fully unload the view, although I a haven't tired adding a callback from my View Model because I'd really like to avoid a callback reference from from my viewmodel to my code beind.

public void SaveDockState()
        {
            if (_dockSite == null)
                return;

            if (_dockSite.ToolWindows.Count == 0)
                return;

            if (LastTimeSaved != null && DateTime.Now - LastTimeSaved < TimeSpan.FromSeconds(1))
                return;

            string xml = s.SaveToString(_dockSite);

            XFile.StringToFile(xml, StateFilePath);

            LastTimeSaved = DateTime.Now;
        }

After trying out a slew of event handlers I think I have this working using the WindowsClosing and WindowsOpening along with a variable that checks to see if the the docksite is loading state so there isn't a recursion bug on load.