Tab into new row DataGridDoubleColumn

Hi,

I want to use the DataGridDoubleColumn like in the following snippet:

public class Point
{
     public double x { get; set; }
     public double y { get; set; }
}

public ObservableCollection<Point> Points { get; set; }

        <datagrid:ThemedDataGrid
                x:Name="dataGrid"
                Grid.Row="1" Grid.Column="0"
                ItemsSource="{Binding Points}"
                AutoGenerateColumns="False"
                CanUserAddRows="True">
            <DataGrid.Columns>
                <datagrideditors:DataGridDoubleColumn Binding="{Binding x}" Header="X" Format="F3" Width="*"/>
                <datagrideditors:DataGridDoubleColumn Binding="{Binding y}" Header="Y" Format="F3" Width="*"/>
            </DataGrid.Columns>
        </datagrid:ThemedDataGrid>

 If the RowHeader of the new row (to add new data) is selected and one presses the TAB-Key some Text-Input is focused. The user can input some values but after hitting Enter or selecting another row no new row gets inserted into the grid. Instead the values stay in the new row "template".

After clicking once on one of the cells of the new row placeholder, the former value is replaced by 0.000 and after two following clicks the user can enter again a value. This time after pressing Enter or selecting another row, a new row is inserted.

How can I fix this behavior? Or is it a Bug?

Best regards,
Ansgar