Selecting a cell of a WPF DataGrid which is inside a RowDetailsTemplate

I am experiencing some strange behavior in my datagrid when I have a second datagrid as a rowdetailstemplate. The main datagrid is bound to my collection of items, and the details datagrid is bound to a collection of subitems contained by an item. Now all of this renders perfectly, but when I want to click on a cell in the SubItemsGrid directly, it first selects the first cell of the row in the main grid in which the SubItemsGrid is contained. I have to click a second time to get to the cell I want to select.

Has anyone experencied this as well? And if so, is there a workaround?

This is my mark-up (partially):

<DataGrid x:Name="ItemGrid" ItemsSource="{Binding Path=Items}" AutoGenerateColumns="False" SelectionUnit="Cell"
          RowDetailsVisibilityMode="Visible" CanUserResizeRows="False" AreRowDetailsFrozen="False" VerticalAlignment="Top"
          CanUserAddRows="False" CanUserDeleteRows="False" VerticalScrollBarVisibility="Hidden">
    <DataGrid.Columns>
        <DataGridTextColumn Header="Column1" Binding="{Binding Path=ID}" Width="350"/>
        <DataGridTextColumn Header="Column2" Binding="{Binding Path=Name}" Width="8开发者_Go百科0"/>
        <DataGridTextColumn Header="Column3" Binding="{Binding Path=Description}" Width="80"/>
    </DataGrid.Columns>
    <DataGrid.RowDetailsTemplate>
        <DataTemplate>
            <DataGrid x:Name="SubItemsGrid" ItemsSource="{Binding Path=SubItems}" AutoGenerateColumns="False"
                      SelectionUnit="Cell" HeadersVisibility="None" Margin="50,0,0,0" VerticalAlignment="Top" CanUserAddRows="False" 
                      CanUserResizeRows="False" CanUserDeleteRows="False" BorderThickness="0">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Column1" Binding="{Binding Path=Name}" Width="300" />
                    <DataGridTextColumn Header="Column2" Binding="{Binding Path=Description}" Width="80"/>
                    <!-- Etc.--> 

---EDIT---

Ok, I came up with the idea to handle the mouse-up event on the SubItemsGrid, and then set the focus to the SubItemsGrid in code, like this:

private void SubItemsGrid_MouseUp(object sender, MouseButtonEventArgs e)
{
   DataGrid selectedGrid = sender as DataGrid;
   if (selectedGrid != null)
   {
       selectedGrid.Focus()
   }
}

Debugging show that the 'Focus' method gets called on the right grid, but I am not getting any visual results. I get the feeling I am very close to the solution however. Anyone?

I fixed this by catching the 'SelectedCellsChanged' event of the SubItemsGrid. In the handler I called 'BeginEdit()' on the grid that raised the event. This indeed put the focus on the clicked cell directly, but also put the cell in edit mode. That's why I called CancelEdit() directly after. This will keep the focus on the cell, but not in edit mode.

private void SubItemsGrid_SelectedCellsChanged(object sender, SelectedCellsChangedEventArgs e)
{
   DataGrid selectedGrid = sender as DataGrid;
   if (selectedGrid != null)
   {
       selectedGrid.BeginEdit();
       selectedGrid.CancelEdit();
   }
}