Binding WP 7.1 Listpicker：所选值显示对象名称而不是属性

我在WP 7.1的ListPicker中遇到了一个问题，我选择的值没有显示绑定，而是显示了作为ItemSource的模型的对象名。但是，当我转到FullModeItemTemplate时，我的绑定工作正常。我已经检查了输出，没有任何绑定错误

这是我的密码

public class TurnoverModel
{
    public string TurnoverId { get; set; }
    public string TurnoverDesc { get; set; }
}

我的模型作为集合传入ItemSource

         <toolkit:ListPicker ItemsSource="{Binding TurnoverList}" Width="350" HorizontalAlignment="Left" Name="turnOverListPicker" SelectionMode="Multiple"}" Header="Turnover" SelectionChanged="OnTurnoverChanged">
            <toolkit:ListPicker.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding TurnoverDesc}"/>
                    </StackPanel>
                </DataTemplate>
            </toolkit:ListPicker.ItemTemplate>
            <toolkit:ListPicker.FullModeItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding TurnoverDesc}" Width="150"/>
                    </StackPanel>
                </DataTemplate>
            </toolkit:ListPicker.FullModeItemTemplate>
        </toolkit:ListPicker>

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也许你可以再详细说明一下？
 <toolkit:ListPicker ItemsSource="{Binding TurnoverList}" Width="350" HorizontalAlignment="Left" Name="turnOverListPicker" SelectionMode="Multiple"}" Header="Turnover" SelectionChanged="OnTurnoverChanged"> 
<toolkit:ListPicker.FullModeItemTemplate>
 <DataTemplate> 
<StackPanel Orientation="Horizontal"> 
<TextBlock Text="{Binding TurnoverDesc}" Width="150"/>
 </StackPanel>
 </DataTemplate>
 </toolkit:ListPicker.FullModeItemTemplate>
 </toolkit:ListPicker> 

 private void OnTurnoverChanged(object sender, SelectionChangedEventArgs e)
    {
     TurnoverModel selecteditem = e.AddedItems[0] as TurnoverModel;
     String turnoverId =selecteditem.TurnoverId;
     String turnoverDesc =selecteditem.TurnoverDesc; 
    }
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