Максимальное пользовательское окно теряет эффект тени

У меня есть пользовательское окно WPF, определяемое как:

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" MinHeight="300" Height="350" MinWidth="600" Width="700"      ResizeMode="CanResizeWithGrip" AllowsTransparency="True" WindowStyle="None">

Я нашел класс онлайн, который создает падение Shadows , показано ниже. Это хорошо работает, даже с видом на размер, пока я не максимизирую окно. Как только я максимизирую окно или измените состояние окна другого окна (например, Visual Studio), я потеряющую тень капли, и я не могу вернуть ее. Любые идеи?

Класс Shadow Shadow:

Public Class DropShadow

Private Shared _handler As EventHandler = New EventHandler(AddressOf window_SourceInitialized)

<DllImport("dwmapi.dll", PreserveSig:=True)> _
Private Shared Function DwmSetWindowAttribute(hwnd As IntPtr, attr As Integer, ByRef attrValue As Integer, attrSize As Integer) As Integer

End Function

<DllImport("dwmapi.dll")> _
Private Shared Function DwmExtendFrameIntoClientArea(hWnd As IntPtr, ByRef pMarInset As Margins) As Integer
End Function

Public Shared Sub DropShadowToWindow(window As Window)
    If Not DropShadow(window) Then
        AddHandler window.SourceInitialized, _handler
        AddHandler window.SizeChanged, New SizeChangedEventHandler(AddressOf windowSizeChanged)
    End If
End Sub

Private Shared Sub window_SourceInitialized(sender As Object, e As EventArgs)
    Dim window As Window = DirectCast(sender, Window)

    DropShadow(window)

    RemoveHandler window.SourceInitialized, _handler
End Sub


Private Shared Function DropShadow(window As Window) As Boolean
    Try
        Dim helper As New WindowInteropHelper(window)
        Dim val As Integer = 2
        Dim ret1 As Integer = DwmSetWindowAttribute(helper.Handle, 2, val, 4)

        If ret1 = 0 Then
            Dim m As New Margins() With { _
             .Bottom = 0, _
             .Left = 0, _
             .Right = 0, _
             .Top = 0 _
            }
            Dim ret2 As Integer = DwmExtendFrameIntoClientArea(helper.Handle, m)
            Return ret2 = 0
        Else
            Return False
        End If
    Catch ex As Exception
        ' Probably dwmapi.dll not found (incompatible OS)
        Return False
    End Try
End Function

Private Shared Sub windowSizeChanged(sender As Object, e As SizeChangedEventArgs)
    Dim window As Window = DirectCast(sender, Window)
    DropShadow(window)
End Sub
End Class