items are not displayed after grouping in ItemsControl
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I've added grouping to ItemsControl:

            <ItemsControl Style="{StaticResource SellingDashboardToDosList}" Grid.Row="2" BorderThickness="1" Background="#C7E8F8" HorizontalAlignment="Stretch" ItemsSource="{Binding ToDoList}" >
                <ItemsControl.GroupStyle>
                    <GroupStyle>
                        <GroupStyle.ContainerStyle>
                            <Style TargetType="GroupItem">
                                <Setter Property="Template">
                                    <Setter.Value>
                                        <ControlTemplate TargetType="GroupItem">
                                            <GroupBox Header="{Binding Name}">
                                                <ItemsPresenter />
                                            </GroupBox>
                                        </ControlTemplate>
                                    </Setter.Value>
                                </Setter>
                            </Style>
                        </GroupStyle.ContainerStyle>
                    </GroupStyle>
                </ItemsControl.GroupStyle>
            </ItemsControl>

Now I see only empty GroupBoxes. I've used Snoop tool to explore the application and I found out that GroupBox ItemPresenters are empty! What could be the reason of it? 

If I remove the grouping from the ItemsControl (the ItemsControl.GroupStyle element), then everything works fine, and I see all items again. I don't need to make any changes to the underlying data context to see all items. The data context (the ItemsSource binging) is of type `SynchronisedObservableCollection<ITodoItemViewModel>` .