Make a GridSplitter react to the visibility of the grid content

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XAML

Silverlight

Hi
I have a grid with three rows. The middle of these three is a GridSplitter control and the content of the bottom row is a stackpanel that has visibility controlled from code (it is basically a notification area).

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="5" />
            <!-- Main content row -->
            <RowDefinition Height="*" />
            <!-- Splitter row -->
            <RowDefinition Height="Auto" />
            <!-- Messages row -->
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>

<!-- content for top of grid.... -->

<!-- Information Messages splitter -->
        <ctrl:GridSplitter x:Name="InformatioMessagesSplitter" Grid.Row="2" Grid.Column="0" 
                           Grid.ColumnSpan="3"
                           VerticalAlignment="Center" HorizontalAlignment="Stretch" 
                           Height="3"
                           removed="Gray" 
                           />

<StackPanel x:Name="InformationMessagesPanel"
                    Grid.Row="0"
                    Height="Auto"
                    removed="LightBlue" 
                    Visibility="{Binding Source={StaticResource MainPageViewModel},Path=InformationMessagePanelVisibility,Mode=OneWay}"
                    >

   <!-- Content goes here -->

</StackPanel>

Now - if the property InformationMessagePanelVisibility is changed, the lower stack panel shows/hides OK and the main content resizes accordingly.

However if the user moves the GridSplitter control then thereafter the property InformationMessagePanelVisibility does show/hide the stack panel but the row sizes don't auto-adjust any more when the lower panel is hidden.

Any ideas?