private static object OnCoerceGroupChanged(DependencyObject o, object newValue)
        {
            ForeignKeyGroupContentControl contentControl = o as ForeignKeyGroupContentControl;

            if (contentControl != null)
            {
                Group currentGroup         = contentControl.Group;
                Group newGroup             = newValue as Group;
                bool  clearContentTemplate = false;

                if ((currentGroup != null) && (newGroup != null))
                {
                    if ((currentGroup.Level == -1) || (newGroup.Level == -1))
                    {
                        clearContentTemplate = true;
                    }
                    // The Group is different, must clear the templates
                    else if (currentGroup.GroupBy != newGroup.GroupBy)
                    {
                        clearContentTemplate = true;
                    }
                }
                else
                {
                    // The Group is null or different, must clear the templates
                    clearContentTemplate = true;
                }

                if (clearContentTemplate)
                {
                    contentControl.ClearValue(ContentControl.ContentTemplateProperty);
                    contentControl.ClearValue(ContentControl.ContentTemplateSelectorProperty);
                }
            }

            return(newValue);
        }