Silverlight DatePicker绑定损坏 – 我该怎么做才能解决这个问题？

我有一个List@L_616_4@绑定到具有datetiR_322_11845@e属性的对象列表.我有一个页面的编辑部分用于更改所选项目.这很好 – 当我更新DatePicker中的日期时,List@L_616_4@显示我更新的日期.

但是,当我然后选择另一个项目时,DatePicker控件也会错误地更新新项目上的日期.

这是我的代码：

C#：

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;

namespace BindingTest
{
    public partial class MainPage
    {
        public MainPage()
        {
            InitializeComponent();

            var vm = new viewmodel();
            DataContext = vm;
        }
    }

    public class viewmodel : INotifyPropertyChanged
    {
        public viewmodel()
        {
            List = new ObservableCollection<Item>();

            for (var n = 0; n < 10; n++)
                List.Add(new Item { Date = datetiR_322_11845@e.Now.AddDays(n) });
        }

        public ObservableCollection<Item> List { get; set; }

        private Item _SELEctedItem;
        public Item SELEctedItem
        {
            get { return _SELEctedItem; }
            set { _SELEctedItem = value; OnPropertyChanged("SELEctedItem"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(String propName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this,new PropertyChangedEventArgs(propName));
        }
    }

    public class Item : INotifyPropertyChanged
    {
        private datetiR_322_11845@e _date;
        public datetiR_322_11845@e Date
        {
            get { return _date; }
            set { _date = value; OnPropertyChanged("Date"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(String propName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this,new PropertyChangedEventArgs(propName));
        }
    }
}

XAML：

<UserControl xmlns:sdk="http://scheR_322_11845@as.microsoft.com/winfx/2006/xaml/presentation/sdk"  x:Class="BindingTest.MainPage"
    xmlns="http://scheR_322_11845@as.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://scheR_322_11845@as.microsoft.com/winfx/2006/xaml">

    <Grid x:Name="LayoutRoot" BACkground="White">
        <Grid.columnDeFinitions>
            <columnDeFinition />
            <columnDeFinition />
        </Grid.columnDeFinitions>

        <List@L_616_4@ Itemssource="{Binding List}" 
                 DisplaymemberPath="Date"
                 SELEctedItem="{Binding SELEctedItem,Mode=TwoWay}" />

        <StackPanel Grid.column="1" DataContext="{Binding SELEctedItem}">
            <TextBlock Text="Date:" />
            <sdk:DatePicker SELEctedDate="{Binding Date,Mode=TwoWay}" />
        </StackPanel>
    </Grid>
</UserControl>

我怎样才能解决这个问题？