The GetNavBarGroup method returns null for NavBarGroup descendants

Hello,
I have a problemm with GetNavBarGroup of the NavBarControl.
In xaml I have something like this:
<dxn:NavBarControl Name="navBar" HorizontalAlignment="Right" DockPanel.Dock="Right">
            <dxn:NavBarControl.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="Add group" Name="miAddGroup" Click="miAddGroup_Click"></MenuItem>
                </ContextMenu>
            </dxn:NavBarControl.ContextMenu>
            <dxn:NavBarControl.View>
                <dxn:SideBarView>
                    <!–dxn:SideBarView.ContextMenu>
                    </dxn:SideBarView.ContextMenu–>
                </dxn:SideBarView>
            </dxn:NavBarControl.View>
            <dxn:NavBarControl.Groups>
                <dxn:NavBarGroup>
                </dxn:NavBarGroup>
            </dxn:NavBarControl.Groups>
        </dxn:NavBarControl>
For getting group, where menu was opened I use code like this "_actionNavBarGroup = navBar.View.GetNavBarGroup(e);" in navBar.ContextMenuOpening += new ContextMenuEventHandler(View_ContextMenuOpening);
Firstly, as you see in navbar in xaml a added empty grour, because <dxn:NavBarGroup></dxn:NavBarGroup>, otherwise context menu doesnt open. Also you can see that I have commented SideBarView.ContextMenu in sidebarview, because I tryed to do this and following in 2 ways of defining menu. (Sorry for my English -)
Secondly. After running a programm I call context menu and call miAddGroup_Click, in actionNavBarGroup I have that empty group. Its ok. But than I clear navBar.Groups and dynamicly add new group:
public class VMCNavBarGroup : NavBarGroup
    {
        public List<Filter> Filters { get; set; }
        public QueryConstructorResultTypes FilterType { get; set; }
    }
…
VMCNavBarGroup nbg = new VMCNavBarGroup();
nbg.Header = qc.GroupName;
foreach (…)
                                {
                                    NavBarItem nbi = new NavBarItem();
                                    nbi.Content = p.NameLoc;
                                    nbg.Items.Add(nbi);
                                }
navBar.Groups.Add(nbg);
After I see on the form my new group an its items. But than I call context menu:
 - clicking on Group header: navBar.View.GetNavBarGroup(e) is null
 - clicking on any item: navBar.View.GetNavBarGroup(e) is null and navBar.View.GetNavBarItem(e) != null
Then I tryed same operetions on menu defined in SideBarView.ContextMenu, result the same.
As I can understand navBar.View.GetNavBarGroup(e) != null, only when groups are defined in xaml, not added dynamicly. But most likely I do something wrong.