ribbon in a grid with row height: excepetion

<ribbon:RibbonWindow 
    x:Class="RibbonTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"                                          
    xmlns:ribbon="http://schemas.actiprosoftware.com/winfx/xaml/ribbon"
    xmlns:RibbonTest="clr-namespace:RibbonTest" Title="MainWindow" Height="350" Width="525">
    <Grid>

        <Grid.RowDefinitions>
            <RowDefinition Height="250"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <RibbonTest:RibbonView Grid.Row="0"/>
        
        <Grid Grid.Row="1" Background="Red"/>
    </Grid>    
</ribbon:RibbonWindow>

<UserControl x:Class="RibbonTest.RibbonView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:ribbon="http://schemas.actiprosoftware.com/winfx/xaml/ribbon"
             mc:Ignorable="d" Loaded="RibbonView_OnLoaded">
<UserControl.Resources>
        <Style x:Key="ImageBackstageTabStyle" TargetType="ribbon:BackstageTab">
            <Setter Property="Header" Value="{Binding Header}"/>
            <Setter Property="KeyTipAccessText" Value="{Binding KeyTipAccessText}"/>            
        </Style>
    </UserControl.Resources>

    <ribbon:Ribbon>
        <ribbon:Ribbon.ApplicationMenu>
            <ribbon:Backstage ItemsSource="{Binding BackstageItems}" ItemContainerStyle="{StaticResource ImageBackstageTabStyle}">                
            </ribbon:Backstage>
        </ribbon:Ribbon.ApplicationMenu>
        <!--all tabs-->
        <ribbon:Ribbon.Tabs >
            <ribbon:Tab Label="Test" KeyTipAccessText="T">
                <ribbon:Group Label="Lock" FontSize="12">
                    <ribbon:StackPanel >
                        <ribbon:Button Label="xx"></ribbon:Button>
                        <ribbon:Button Label="YY"></ribbon:Button>
                    </ribbon:StackPanel>
                    </ribbon:Group>
            </ribbon:Tab>
            <ribbon:Tab Label="XX" KeyTipAccessText="U">
                <ribbon:Group Label="Lock" FontSize="12">
                    <ribbon:StackPanel >
                        <ribbon:Button Label="KK"></ribbon:Button>
                        <ribbon:Button Label="TES"></ribbon:Button>
                    </ribbon:StackPanel>
                </ribbon:Group>
            </ribbon:Tab>
        </ribbon:Ribbon.Tabs>
    </ribbon:Ribbon>
</UserControl>