Ошибка в шаблоне подменю в WPF

Я использую шаблон заголовочного меню, а также шаблон подменю-заголовка. Главное меню заголовка Работает нормально, но подменю не работает. Не показывает.

Мой код Wpf XAML (шаблон заголовка подменю):

    <ControlTemplate x:Key = "{x:Static MenuItem.SubmenuHeaderTemplateKey}"  TargetType = "{x:Type MenuItem}">
        <Border x:Name = "Border" BorderThickness = "1">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width = "Auto"    SharedSizeGroup = "Icon" />
                    <ColumnDefinition Width = "*" />
                    <ColumnDefinition Width = "Auto"   SharedSizeGroup = "Shortcut" />
                    <ColumnDefinition Width = "13" />
                </Grid.ColumnDefinitions>
                <ContentPresenter x:Name = "Icon"  Margin = "6,0,6,0" VerticalAlignment = "Center"  ContentSource = "Icon" />
                <ContentPresenter x:Name = "HeaderHost" Grid.Column = "1" ContentSource = "Header"  RecognizesAccessKey = "True" />
                <TextBlock x:Name = "InputGestureText"  Grid.Column = "2" Text = "{TemplateBinding InputGestureText}" Margin = "5,2,2,2" DockPanel.Dock = "Right" />
                <Path Grid.Column = "3" HorizontalAlignment = "Center" VerticalAlignment = "Center" Data = "M 0 0 L 0 7 L 4 3.5 Z">
                    <Path.Fill>
                        <SolidColorBrush Color = "White"  />
                    </Path.Fill>
                </Path>
                <Popup x:Name = "Popup" Placement = "Right" HorizontalOffset = "-4" IsOpen = "{TemplateBinding IsSubmenuOpen}" AllowsTransparency = "True" Focusable = "False" PopupAnimation = "Fade">
                    <Border x:Name = "SubmenuBorder" SnapsToDevicePixels = "True" Background = "RoyalBlue"  BorderThickness = "1">
                        <Border.BorderBrush>
                            <SolidColorBrush Color = "RoyalBlue" />
                        </Border.BorderBrush>
                    </Border>
                </Popup>
            </Grid>
        </Border>
        <ControlTemplate.Triggers>
            <Trigger Property = "Icon" Value = "{x:Null}">
                <Setter TargetName = "Icon"   Property = "Visibility"  Value = "Collapsed" />
            </Trigger>
            <Trigger Property = "IsHighlighted" Value = "true">
                <Setter Property = "Background" TargetName = "Border">
                    <Setter.Value>
                        <LinearGradientBrush EndPoint = "0.5,1"  StartPoint = "0.5,0">
                            <GradientStop Color = "Transparent" Offset = "0" />
                            <GradientStop Color = "DeepSkyBlue" Offset = "1" />
                        </LinearGradientBrush>
                    </Setter.Value>
                </Setter>
                <Setter Property = "BorderBrush" TargetName = "Border">
                    <Setter.Value>
                        <LinearGradientBrush EndPoint = "0.5,1" StartPoint = "0.5,0">
                            <GradientStop Color = "DeepSkyBlue"   Offset = "0" />
                            <GradientStop Color = "Transparent"  Offset = "1" />
                        </LinearGradientBrush>
                    </Setter.Value>
                </Setter>
            </Trigger>
            <Trigger SourceName = "Popup" Property = "AllowsTransparency" Value = "True">
                <Setter TargetName = "SubmenuBorder" Property = "CornerRadius" Value = "4" />
                <Setter TargetName = "SubmenuBorder" Property = "Padding" Value = "0,3,0,3" />
            </Trigger>
            <Trigger Property = "IsEnabled" Value = "false">
                <Setter Property = "Foreground">
                    <Setter.Value>
                        <SolidColorBrush Color = "DeepPink" />
                    </Setter.Value>
                </Setter>
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>

Применить к дизайну:

 <Grid>
    <Menu Height = "24" VerticalAlignment = "Top" Style = "{DynamicResource HiMicrosoft}">
        <MenuItem Header = "Media" Width = "48">
            <MenuItem Header = "Open Files" Template = "{DynamicResource MI }"/>
            <MenuItem Header = "Open Folder" Template = "{DynamicResource MI }"/>
            <MenuItem Header = "Open Playlist" Template = "{DynamicResource MI }"/>
            <MenuItem Header = "Open Recent" Template = "{DynamicResource MI }"/>
            <Separator Style = "{DynamicResource {x:Static MenuItem.SeparatorStyleKey} }"/>
            <MenuItem Header = "Hide" Template = "{DynamicResource MI }"/>
            <MenuItem Header = "Exit" Template = "{DynamicResource MI }"/>
        </MenuItem>
        <MenuItem Header = "Playback" >
            <MenuItem Header = "Play/Pause" Template = "{DynamicResource MI }"/>
            <MenuItem Header = "Stop" Template = "{DynamicResource MI }"/>
            <Separator Style = "{DynamicResource {x:Static MenuItem.SeparatorStyleKey} }" />
            <MenuItem Header = "Speed" Template = "{DynamicResource MI }">
                <MenuItem  Header = "Stop"  Template = "{DynamicResource {x:Static MenuItem.SubmenuHeaderTemplateKey}}"/>
            </MenuItem>
        </MenuItem>
    </Menu>
</Grid>

И вот окончательный снимок экрана:

Когда я нажимаю на скорость, он ничего не показывает. Я не могу определить ошибку или, возможно, использовал неправильный метод.

Любая помощь будет оценена!

Если хотите, я могу предоставить более подробную информацию. Просто прокомментируйте ниже.

Заранее спасибо!