WPF-DropShadowEffect在设计时可见，但在运行时不可见？

Question

我正在尝试在WPF应用程序的主窗口上创建外部发光效果。

这是主窗口的XAML：

<Window x:Class="UITestA.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:shell="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:local="clr-namespace:UITestA" 
        mc:Ignorable="d"
        WindowStyle="None"
        AllowsTransparency="True"
        ResizeMode="CanResizeWithGrip" 
        WindowStartupLocation="CenterScreen"
        Background="#FF302C2C"
        Title="MainWindow" Height="450" Width="800" MouseDown="Window_MouseDown">

    <Window.Effect>
        <DropShadowEffect Color="Black" BlurRadius="20" Direction="-90" RenderingBias="Quality" ShadowDepth="4"/>
    </Window.Effect>

    <Window.Style>
        <Style TargetType="{x:Type Window}">
            <Setter Property="shell:WindowChrome.WindowChrome">
                <Setter.Value>
                    <shell:WindowChrome ResizeBorderThickness="4" CaptionHeight="35"  CornerRadius="0" GlassFrameThickness="0"/>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Style>

    <Grid Background="#FF302C2C" >

        <Grid VerticalAlignment="Top" Background="#FF4D4848">

            <StackPanel Height ="35" WindowChrome.IsHitTestVisibleInChrome="True" VerticalAlignment="Center" HorizontalAlignment="Right" Orientation="Horizontal">

                <Button Width="35" Name="MinimizeButton" Style="{StaticResource CaptionButtonMinMax}">
                    <Image Source="{StaticResource pngMinimize}" Stretch="None"/>
                </Button>

                <Button Width="35" Name="MaximazeButton" Style="{StaticResource CaptionButtonMinMax}">
                    <Image Source="{StaticResource pngMaximize}" Stretch="None"/>
                </Button>

                <Button Width="35" Name="CloseButton" Style="{StaticResource CaptionButtonClose}">
                    <Image Source="{StaticResource pngClose}" Stretch="None"/>
                </Button>

            </StackPanel>

        </Grid>

    </Grid>

</Window>

在设计器中我可以看到DropShadowEffect，但是当我运行应用程序时却不显示！

我不明白我在做什么错，所以有人可以帮助我纠正这个问题吗？