I have a xamDatagrid placed in a grid control, on a user control, with some grid splitters for resizing my columns and rows...

Why is my horizontal scrollbar not showing up at all ever?

<UserControl x:Class="WorksheetControl"
             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:ig="http://infragistics.com/DataPresenter"
             mc:Ignorable="d"
             d:DesignHeight="500" d:DesignWidth="300">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="300"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="300"/>
        </Grid.RowDefinitions>
        <ListBox Name="lbFiles" Grid.Row="0" Grid.Column="0" Margin="0,0,0,5">

        </ListBox>

        <ig:XamDataGrid Grid.Row="1" Grid.Column="0" DataSource="{Binding CalculatedValues}">
            <ig:XamDataGrid.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="Add Calculated Value" Click="AddCV_Click"/>
                </ContextMenu>
            </ig:XamDataGrid.ContextMenu>
            <ig:XamDataGrid.ViewSettings>
                <ig:GridViewSettings />
            </ig:XamDataGrid.ViewSettings>
            <ig:XamDataGrid.FieldLayoutSettings>
                <ig:FieldLayoutSettings AutoGenerateFields="False" SelectionTypeCell="Default" SelectionTypeField="Single" SelectionTypeRecord="Extended" />
            </ig:XamDataGrid.FieldLayoutSettings>
            <ig:XamDataGrid.FieldLayouts >
                <ig:FieldLayout IsDefault="True" >
                    <ig:Field Name="Name" Label="{Binding Name}"/>
                    <ig:Field Name="Value" Label="{Binding Value}"/>
                    <ig:Field Name="Units" Label="{Binding Units}" />
                </ig:FieldLayout>
            </ig:XamDataGrid.FieldLayouts>
            <!-- Enable field selection and disable cell editing-->
            <ig:XamDataGrid.FieldSettings>
                <ig:FieldSettings LabelClickAction="SelectField" AllowEdit="True" CellClickAction="SelectRecord" CellContentAlignment="LabelAboveValueAlignCenter" />
            </ig:XamDataGrid.FieldSettings>
        </ig:XamDataGrid>
        <GridSplitter ResizeDirection="Rows" Grid.Column="0" Grid.Row="0" Width="Auto" Height="5" HorizontalAlignment="Stretch" VerticalAlignment="Bottom"/>
        <GridSplitter Grid.Column="1" Grid.RowSpan="2" Width="5" HorizontalAlignment="Left" />
    </Grid>
</UserControl>