title: DeferRefresh is not allowed during an AddNew or EditItem transaction
body: <p>I have a Window containing 2 DataGrids. And if I click from one specific column in the first DataGrid into any column of the other DataGrid, then I get the error</p>
  
  <blockquote>
    <p>DeferRefresh is not allowed during an AddNew or EditItem transaction</p>
  </blockquote>
  
  <p>What is going wrong here?</p>
  
  <p>The first DataGrid is</p>
  
  <pre><code>&lt;DataGrid x:Name="FirstDataGrid"
            ItemsSource="{Binding Parts, Mode=TwoWay}"
            SelectedItem="{Binding SelectedPart, Mode=TwoWay}"
            CellEditEnding="DataGrid_OnCellEditEnding" &gt;
       &lt;i:Interaction.Behaviors&gt;
            &lt;views:ScrollIntoViewBehavior /&gt;
       &lt;/i:Interaction.Behaviors&gt;
            &lt;DataGrid.Resources&gt;
                 &lt;Style TargetType="{x:Type DataGridCell}"&gt;
                     &lt;EventSetter Event="PreviewMouseLeftButtonDown" Handler="DataGridCell_PreviewMouseLeftButtonDown"&gt;&lt;/EventSetter&gt;
                 &lt;/Style&gt;
            &lt;/DataGrid.Resources&gt;
        &lt;DataGrid.Columns&gt;
            &lt;DataGridTemplateColumn&gt;
                      &lt;DataGridTemplateColumn.CellTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;ItemsControl ItemsSource="{Binding Identifications, Mode=OneWay}"&gt;
                                  &lt;ItemsControl.ItemsPanel&gt;
                                      &lt;ItemsPanelTemplate&gt;
                                          &lt;StackPanel Orientation="Horizontal"/&gt;
                                      &lt;/ItemsPanelTemplate&gt;
                                  &lt;/ItemsControl.ItemsPanel&gt;
                                  &lt;ItemsControl.ItemTemplate&gt;
                                      &lt;DataTemplate&gt;
                                          &lt;TextBlock Margin="5,0,0,0"&gt;
                                              &lt;Hyperlink NavigateUri="{Binding ArticleNumber, Mode=OneWay}" 
                                                          Command="{Binding ElementName=PartDataGrid, Path=DataContext.OpenIdentificationCommand}" CommandParameter="{Binding}" &gt;                                    
                                                  &lt;TextBlock Text="{Binding ArticleNumber, Mode=OneWay}"/&gt;
                                              &lt;/Hyperlink&gt;
                                          &lt;/TextBlock&gt;
                                      &lt;/DataTemplate&gt;
                                  &lt;/ItemsControl.ItemTemplate&gt;
                              &lt;/ItemsControl&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/DataGridTemplateColumn.CellTemplate&gt;
                  &lt;/DataGridTemplateColumn&gt;
        &lt;/DataGrid.Columns&gt;
  &lt;/DataGrid&gt;
  </code></pre>
  
  <p>The second DataGrid does not matter since I can click on any column to produce the error.</p>