New Post: Basic RichTextBox usage - .Text Property does not update

I also had the same problem,and It seems that the nestest version doesn't work.Finally I soved this problem by this way:

this.SetValue(Xceed.Wpf.Toolkit.RichTextBox.TextProperty, TextFormatter.GetText(this.Document));
this.RaiseEvent(new System.Windows.RoutedEventArgs(System.Windows.UIElement.LostFocusEvent, this));