I use the "RibbonWindowSample" did a test and found to be a problem
1.First, I modified the "UserControlMVVM.xaml" file
......
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="30" />
</Grid.RowDefinitions>
<ribbon:Ribbon x:Name="ribbon"
Grid.Row="0"
ItemsSource="{Binding Source={x:Static data:ViewModel.RibbonData},Path=TabDataCollection}"
ContextualTabGroupsSource="{Binding Source={x:Static data:ViewModel.RibbonData},Path=ContextualTabGroupDataCollection}">
<ribbon:Ribbon.ApplicationMenu>
 
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