I keep getting this button in the header, I can click on the button to select all rows. This misaligns the data from the header. Any ideas? Thanks in Advance.

Datagrid image via link:

http://picasaweb.google.com/lh/photo/CahvlINknhL5ykIW2zCfIw?feat=directlink

<dg:DataGrid.Columns>
    <dg:DataGridTextColumn Header="Description" Width=".5*"
                           Binding="{Binding Description}">
    </dg:DataGridTextColumn>
    <dg:DataGridTextColumn Header="Type" Width="100" Binding="{Binding Type}">
    </dg:DataGridTextColumn>
    <dg:DataGridTextColumn Header="Amount $" Width="100" Binding="{Binding Amount}">
    </dg:DataGridTextColumn>
    <dg:DataGridTextColumn Header="Effective From Date" Width="100" Binding="{Binding EffectiveFromDate}"
                           IsReadOnly="True">
    </dg:DataGridTextColumn>
    <dg:DataGridTextColumn Header="Effective To Date" Width="100" Binding="{Binding EffectiveToDate}"
                           IsReadOnly="True">
    </dg:DataGridTextColumn>
    <dg:DataGridTextColumn Header="Status" Width="100" Binding="{Binding Status}">
    </dg:DataGridTextColumn>
</dg:DataGrid.Columns>