Why is OnElementPropertyChanged not called on ViewRenderer

I've derived a CustomPicker from Picker and added some bindable properties like

public class CustomPicker : Picker
{
    public static readonly BindableProperty PickerTextColorProperty = BindableProperty.Create("PickerTextColor", typeof(Color), typeof(CustomPicker), Color.Default);
    public Color PickerTextColor
    {
            get { return (Color)GetValue(PickerTextColorProperty); }
            set { SetValue(PickerTextColorProperty, value); }
    }
}

I've made a custom iOS renderer like

[assembly:ExportRenderer(typeof(CustomPicker), typeof(CustomPickerRenderer))]
namespace MyApp
{
        public class CustomPickerRenderer : ViewRenderer<CustomPicker, UIResponderButton>
        {
            ..
        }
}

I'm listning on the properties change with

protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    base.OnElementPropertyChanged(sender, e);
    ..
}

But the code is not triggered for the new CustomPicker properties. Only for the derived Picker properties.

Anyone got an idea why?

I'm using version 1.2.3