WPF / WindowChrome / Blur Behind "glitchy"

Question

Trying to use WPF / Blur Behind / WindowChrome for my app. I want blur behind, window resize, window drag and drop shadow.

When I run in the debugger F5, the glass appears for about a second before the WPF window finally paints. How do I fix this?

Xaml:

<Window x:Class="WpfApp3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        ResizeMode="CanResizeWithGrip"
        WindowStyle="None"
        Background="Transparent"
        WindowStartupLocation="CenterScreen"
        Title="MainWindow" Height="450" Width="800">
    <WindowChrome.WindowChrome>
        <WindowChrome CaptionHeight="24" GlassFrameThickness="1" UseAeroCaptionButtons="False" />
    </WindowChrome.WindowChrome>
    <Grid Background="#D000FF00">

    </Grid>
</Window>

C#:

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Interop;

namespace WpfApp3
{
    internal enum AccentState
    {
        ACCENT_DISABLED = 0,
        ACCENT_ENABLE_GRADIENT = 1,
        ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
        ACCENT_ENABLE_BLURBEHIND = 3,
        ACCENT_INVALID_STATE = 4
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct AccentPolicy
    {
        public AccentState AccentState;
        public int AccentFlags;
        public int GradientColor;
        public int AnimationId;
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct WindowCompositionAttributeData
    {
        public WindowCompositionAttribute Attribute;
        public IntPtr Data;
        public int SizeOfData;
    }

    internal enum WindowCompositionAttribute
    {
        // ...
        WCA_ACCENT_POLICY = 19
        // ...
    }

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        [DllImport("user32.dll")]
        internal static extern int SetWindowCompositionAttribute(IntPtr hwnd, ref WindowCompositionAttributeData data);

        public MainWindow()
        {

            InitializeComponent();
            this.Loaded += MainWindow_Loaded;
        }

        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            EnableBlur();
        }

        internal void EnableBlur()
        {
            var windowHelper = new WindowInteropHelper(this);

            var accent = new AccentPolicy();
            accent.AccentState = AccentState.ACCENT_ENABLE_BLURBEHIND;

            var accentStructSize = Marshal.SizeOf(accent);

            var accentPtr = Marshal.AllocHGlobal(accentStructSize);
            Marshal.StructureToPtr(accent, accentPtr, false);

            var data = new WindowCompositionAttributeData();
            data.Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY;
            data.SizeOfData = accentStructSize;
            data.Data = accentPtr;

            SetWindowCompositionAttribute(windowHelper.Handle, ref data);

            Marshal.FreeHGlobal(accentPtr);
        }
    }
}