Notifying about clearselection

[John]

I have a property

private const string FirstFacingHandlerIdPropertyName = "FirstFacingHandlerId";
        public int FirstFacingHandlerId
        {
            get { return _firstFacingHandlerId; }
            set
            {
                if (_firstFacingHandlerId != value)
                {
                    _firstFacingHandlerId = value;
                    OnPropertyChanged(FirstFacingHandlerIdPropertyName);
                }
            }
        }

And it's binded in this way:

<telerik:GridViewDataColumn DataMemberBinding="{Binding FirstFacingHandlerId}" Header="1st" IsReadOnly="True">
                          <telerik:GridViewDataColumn.CellTemplate>
                              <DataTemplate>
                                  <telerik:RadComboBox SelectedValuePath="HandlerId" ClearSelectionButtonContent="SomeText" ClearSelectionButtonVisibility="Visible"
                                               SelectedValue="{Binding FirstFacingHandlerId, Mode=TwoWay}" x:Name="radComboBoxFirstFacingHandler" SelectionChanged="radComboBoxFirstFacingHandler_SelectionChanged"
                                               ItemsSource="{Binding Source={StaticResource Locator}, Path=ShowroomLog.Handlers}"
                                               DisplayMemberPath="HandlerName" />
                              </DataTemplate>
                          </telerik:GridViewDataColumn.CellTemplate>
                      </telerik:GridViewDataColumn>

And this is Handlers property:

public ObservableCollection<Handler> Handlers
       {
           get
           {
               if (_handlers.Count == 0)
               {
                   GetHandlers();
               }

               return _handlers;
           }
           set { this._handlers = value; }
       }

The problem is that using ClearSelection button doesn't set my property.
I see that it's set value of RadComboBox

private void radComboBoxFirstFacingHandler_SelectionChanged(object sender, SelectionChangedEventArgs e)
       {
           var X = ((RadComboBox) sender).SelectedValue;
       }

for x I get null

When I change user to another user it works correctly (It sets me property FirstFacingHandlerId).

How can I handle with this?