Why does this not render correctly?

<sdk:DataGrid AutoGenerateColumns="False" Height="438" HorizontalAlignment="Left" Margin="12,183,0,0" Name="dataGridWorkingGrid" VerticalAlignment="Top" Width="856" ClipboardCopyMode="IncludeHeader" CanUserReorderColumns="False" CanUserResizeColumns="False">
    <sdk:DataGrid.Columns>
        <sdk:DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Header="BatchID" IsReadOnly="True" Visibility="Collapsed" Width="Auto" Binding="{Binding BatchID}"/>
            <sdk:DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Header="Transaction Date" IsReadOnly="True" Width="100" Binding="{Binding TransactionDate, StringFormat='MM/dd/yyyy'}">
                <sdk:DataGridTextColumn.HeaderStyle>
                    <Style TargetType="TextBlock">
                        <Setter Property="TextWrapping" Value="Wrap"/>
                    </Style>
                </sdk:DataGridTextColumn.HeaderStyle>
            </sdk:DataGridTextColumn>
        <sdk:DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Header="Merchant Name" IsReadOnly="True" Width="200" Binding="{Binding MerchantName}"/>
    </sdk:DataGrid.Columns>
</sdk:DataGrid>