Telerik Radwindow render incompletely when setting AllowTransparency="False"

I has a question about radwindow rendering.

When I set the AllowTransparency="False" and ShowInTaskbar="True", I switch the window by clicking the taskbar icon, the window just rendering the Windows Title and other parts is hidden. I must drag or resize it to recover.

the complete window: the incomplete window:

So if I set AllowTransparency = True will solve it, but the windows will become slow when drag it.

The telerik version is 2019.3.1023.300, dotnet version: 3.1, windows OS: windown 10 1903

RadWindow Code:

<telerik:RadWindow x:Class="TelerikTest.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:local="clr-namespace:TelerikTest"
                   xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
                   xmlns:navigation="clr-namespace:Telerik.Windows.Controls.Navigation;assembly=Telerik.Windows.Controls.Navigation"
                   mc:Ignorable="d"
                   Width="1024"
                   Height="768"
                   MinWidth="800"
                   MinHeight="600"
                   WindowStartupLocation="CenterScreen"
                   navigation:RadWindowInteropHelper.AllowTransparency="False"
                   navigation:RadWindowInteropHelper.ShowInTaskbar="True"
                   >
    <telerik:RadWindow.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/System.Windows.xaml" />
                <ResourceDictionary
                    Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.Navigation.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </telerik:RadWindow.Resources>

    <telerik:RadWindow.Style>
        <StaticResource ResourceKey="RadWindowStyle" />
    </telerik:RadWindow.Style>
    <Grid>

    </Grid>
</telerik:RadWindow>

This was a bug in the RadWindow control. It is not marked in the release notes, but it was fixed with the R1 2020 release of Telerik UI for WPF (version 2020.1.115).