WPF RibbonApplicationSplitMenuItem Header

Could you tell me, why I can't see Header in Ribb开发者_开发技巧onApplicationSplitMenuItem? I have next code:

<r:Ribbon.ApplicationMenu>
            <r:RibbonApplicationMenu>
                <r:RibbonApplicationMenu.Command>
                    <r:RibbonCommand LabelTitle="Test"/>
                </r:RibbonApplicationMenu.Command>

                <r:RibbonApplicationSplitMenuItem Header="**I can't see this text**">                        
                    <r:RibbonApplicationMenuItem>
                        <r:RibbonApplicationMenuItem.Command>
                            <r:RibbonCommand LabelTitle="New"
                                             Executed="New" />
                        </r:RibbonApplicationMenuItem.Command>
                    </r:RibbonApplicationMenuItem>

..............

Try this

   <Ribbon:Ribbon Grid.Row="0">
            <Ribbon:Ribbon.ApplicationMenu>
                <Ribbon:RibbonApplicationMenu>
                    <Ribbon:RibbonApplicationMenu.AuxiliaryPaneContent>
                        <Grid MinHeight="500">
                            <Grid.RowDefinitions>
                                <RowDefinition Height="30"/>
                                <RowDefinition Height="*"/>
                            </Grid.RowDefinitions>
                            <Border Grid.Row="0" BorderBrush="DarkBlue" BorderThickness="0,0,0,1">
                                <StackPanel  
                                        Orientation="Vertical">
                                    <Label Foreground="DarkBlue" HorizontalAlignment="Left" VerticalAlignment="Center" HorizontalContentAlignment="Left"
                                       VerticalContentAlignment="Center" Content="Hello World"  />
                                </StackPanel>
                            </Border>
                            <ListBox Grid.Row="1">
                                <ListBoxItem>List Box Item 1</ListBoxItem>
                                <ListBoxItem>List Box Item 2</ListBoxItem>
                                <ListBoxItem>List Box Item 3</ListBoxItem>
                                <ListBoxItem>List Box Item 4</ListBoxItem>
                            </ListBox>
                        </Grid>
                    </Ribbon:RibbonApplicationMenu.AuxiliaryPaneContent>
                    <Ribbon:RibbonApplicationMenuItem Header="Hello _Ribbon"   ImageSource="Images\LargeIcon.png"/>
                    <Ribbon:RibbonApplicationMenuItem Header="Hello _Ribbon"   ImageSource="Images\LargeIcon.png"/>
                    <Ribbon:RibbonApplicationMenuItem Header="Hello _Ribbon"   ImageSource="Images\LargeIcon.png"/>
                </Ribbon:RibbonApplicationMenu>

            </Ribbon:Ribbon.ApplicationMenu>


        </Ribbon:Ribbon>

It gives me this