WPF ContextMenu吞下所有鼠标事件

我发现了一个bug，我不明白为什么会这样。我有DataGrid。在鼠标左键上点击我要打开上下文菜单。我做到了。它工作得很好，直到我开始点击随机的DataGrid的细胞(每次ContextMenu关闭并重新出现在新的地方)。但在某一刻发生的事情和ContextMenu较新的显示(和窗口不响应任何鼠标事件，如点击按钮等)…直到我将光标移出窗口并返回它(或按Alt或F10)。

下面是一些代码:
ContextMenu (inside <DataGrid.Resources>)

<ContextMenu Style="{StaticResource DefaultContextMenuStyle}" x:Key="cm"
     DataContext="{Binding Data, Source={StaticResource WindowViewModel}}">
</ContextMenu>

DataGrid专栏:

<DataGridTemplateColumn Header="TestHeader" Width="*">
    <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <DockPanel ContextMenu="{StaticResource cm}" VerticalAlignment="Stretch" Background="Transparent">
                <i:Interaction.Behaviors>
                    <local:OpenContextMenuLeftBehavior />
                </i:Interaction.Behaviors>
                <TextBlock Style="{StaticResource TextVCenteredCellStyle}" Text="{Binding LPU}" />
            </DockPanel>
        </DataTemplate>
    </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

和行为打开上下文菜单:

public class OpenContextMenuLeftBehavior : Behavior<FrameworkElement>
{
    protected override void OnAttached()
    {
        AssociatedObject.PreviewMouseUp += OpenContextMenu;
    }
    protected override void OnDetaching()
    {
        AssociatedObject.PreviewMouseUp -= OpenContextMenu;
    }
    void OpenContextMenu(object sender, MouseButtonEventArgs e)
    {
        if (e.ChangedButton == MouseButton.Left) {
            FrameworkElement Sender = sender as FrameworkElement;
            Sender.ContextMenu.PlacementTarget = Sender;
            Sender.ContextMenu.IsOpen = true;
        }
    }
}

当我发现这个bug时，我试图用Snoop WPF找到一些信息。这里有一些信息:

1. 在糟糕的事情发生之前，点击cell是这样的:
   

2. 坏事发生后:
   坏事之后
   第一个事件发生在弹出(上下文菜单部分?)，它不属于窗口可视化树。
   

当我把鼠标移出主窗口时，这个弹出窗口似乎伸展了整个主窗口并关闭。

我在那个bug上浪费了2天时间，这就是我能找到的全部。
请帮帮我。

编辑:我创建了一个最小的例子:

XAML:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:local="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <DataGrid x:Name="dg1" IsReadOnly="True">
            <DataGrid.Columns>
                <DataGridTemplateColumn Width="*">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <DockPanel>
                                <i:Interaction.Behaviors>
                                    <local:OpenContextMenuLeftBehavior />
                                </i:Interaction.Behaviors>
                                <DockPanel.ContextMenu>
                                    <ContextMenu>
                                        <MenuItem Header="123456"></MenuItem>
                                    </ContextMenu>
                                </DockPanel.ContextMenu>
                                <TextBlock Text="123" />
                            </DockPanel>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

背后的代码:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        dg1.ItemsSource = new List<int>()
        {
            1,2,3,4,5,6,7,8,9,0
        };
    }
}
public class OpenContextMenuLeftBehavior : Behavior<FrameworkElement>
{
    protected override void OnAttached()
    {
        AssociatedObject.PreviewMouseUp += OpenContextMenu;
    }
    protected override void OnDetaching()
    {
        AssociatedObject.PreviewMouseUp -= OpenContextMenu;
    }
    void OpenContextMenu(object sender, MouseButtonEventArgs e)
    {
        if (e.ChangedButton == MouseButton.Left) {
            FrameworkElement Sender = sender as FrameworkElement;
            if (Sender != null) {
                Sender.ContextMenu.PlacementTarget = Sender;
                Sender.ContextMenu.IsOpen = true;
                Sender.ContextMenu.UpdateLayout();
            }
        }
    }
}

要重现这个bug，只需快速点击不同的单元格

                    Sender.ContextMenu.IsOpen = true;
                    Sender.ContextMenu.PreviewMouseUp += ContextMenu_PreviewMouseUp;

    private void ContextMenu_PreviewMouseUp(object sender, MouseButtonEventArgs e)
    {
        var Sender = (sender as ContextMenu);
        if (Sender != null)
        {
            Sender.IsOpen = true;
            e.Handled = true;
        }
    }