We have tested your scenario by updating the marked zone on a button click and it works as expected on our side.Please, consider the following code snippet :
private void button_Click(object sender, RoutedEventArgs e)
MarkedZone markedzone = this.radChart.DefaultView.ChartArea.Annotations as MarkedZone;
markedzone.StartY = 0;
markedzone.EndY = 1.5;
markedzone.Background = new SolidColorBrush(Color.FromArgb(255, 248, 109, 90));
Alternatively, you can clear all annotations on button click and set new ones if needed.
Hope this helps.
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>