Gridsplitter ignores minwidth of columns

Try this instead for three columns that have minwidth set to 80. Use * instead of specifying exact width when using gridsplitters.

<ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Hidden">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" MinWidth="80" />
            <ColumnDefinition Width="5"/>
            <ColumnDefinition Width="*" MinWidth="80"/>
            <ColumnDefinition Width="5"/>
            <ColumnDefinition Width="*" MinWidth="80"/>
        </Grid.ColumnDefinitions>
        <TextBlock Grid.Column="0" Text="{Binding Path=ActualWidth, RelativeSource={RelativeSource Self}}" />
        <GridSplitter Grid.Column="1"  VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Background="Red" />
        <TextBlock Grid.Column="2" Text="{Binding Path=ActualWidth, RelativeSource={RelativeSource Self}}" />
        <GridSplitter Grid.Column="3"   VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Background="Red" />
        <TextBlock Grid.Column="4" Text="{Binding Path=ActualWidth, RelativeSource={RelativeSource Self}}" />
    </Grid>
</ScrollViewer>