inkcanvas problem z cofnij i wróc

Do inkcanvasa w wpfie chce dodać operacje cofnij i wróc. Prawie działa, jednak jak zrobie cofnij coś narysuje to potem mogę przywrócic to co cofnąłem przed narysowaniem, a tak nie powinno być.

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using PluginInterfaceNamespace;

namespace PluginApp
{
    public partial class MainWindow : Window
    {

        System.Windows.Ink.StrokeCollection addedStrokes;
        System.Windows.Ink.StrokeCollection removedStrokes;
        public MainWindow()
        {
            InitializeComponent();

            InkCanvas.DefaultDrawingAttributes.Color = Colors.Black;
            InkCanvas.Strokes.StrokesChanged += Strokes_StrokesChanged;
            addedStrokes = new System.Windows.Ink.StrokeCollection();
            removedStrokes = new System.Windows.Ink.StrokeCollection();

            addMenuItems();
        }

        private void Strokes_StrokesChanged(object sender, System.Windows.Ink.StrokeCollectionChangedEventArgs e)
        {
            /*if (handle)
            {
                _added = e.Added;
                _removed = e.Removed;
            }*/
            if (e.Added != null)
            {
                addedStrokes.Add(e.Added);
                removedStrokes.Clear();
            }
        }

        private void Undo_Click(object sender, RoutedEventArgs e)
        {

            if (addedStrokes.Count != 0)
            {
                removedStrokes.Add(addedStrokes.ElementAt(addedStrokes.Count - 1));
                addedStrokes.RemoveAt(addedStrokes.Count - 1);
            }

            InkCanvas.Strokes = addedStrokes;
        }

        private void Redo_Click(object sender, RoutedEventArgs e)
        {

            if (removedStrokes.Count != 0)
            {
                addedStrokes.Add(removedStrokes.ElementAt(removedStrokes.Count - 1));
                removedStrokes.RemoveAt(removedStrokes.Count - 1);
            }

            InkCanvas.Strokes = addedStrokes;
        }
    }
}

teraz działa

Stack<System.Windows.Ink.StrokeCollection> addedStrokes;
        Stack<System.Windows.Ink.StrokeCollection> removedStrokes;

addedStrokes = new Stack<System.Windows.Ink.StrokeCollection>();
            removedStrokes = new Stack<System.Windows.Ink.StrokeCollection>();

private void Strokes_StrokesChanged(object sender, System.Windows.Ink.StrokeCollectionchangedEventArgs e)
        {
            if (handle)
            {
                addedStrokes.Push(e.Added);
                removedStrokes.Push(e.Removed);
                if (e.Added != null)
                {
                    removedStrokes.Clear();
                }
            }
        }

        private void Undo_Click(object sender, RoutedEventArgs e)
        {
            if (addedStrokes.Count != 0)
            {
                handle = false;
                var stroke = addedStrokes.Pop();
                InkCanvas.Strokes.Remove(stroke);
                removedStrokes.Push(stroke);
                handle = true;
            }
        }

        private void Redo_Click(object sender, RoutedEventArgs e)
        {
            if (removedStrokes.Count != 0)
            {
                handle = false;
                var stroke = removedStrokes.Pop();
                InkCanvas.Strokes.Add(stroke);
                addedStrokes.Push(stroke);
                handle = true;
            }
        }