Reproduce performance issue in CalcBinding

-----
MainWindow.xaml.cs:   
-----
    class Person
    {
        public int Age { get; set; }
    }
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new ObservableCollection<Person>(Enumerable.Range(1,1000).Select(i => new Person {Age=i})) ;
        }
    }
    
-----
MainWindow.xaml:
-----
    
    <Window x:Class="WpfApplication5.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfApplication5="clr-namespace:WpfApplication5"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <ItemsControl ItemsSource="{Binding}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                   <wpfApplication5:MyUserControl/>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </Grid>
</Window>


-----
MyUserControl.xaml:
-----

<UserControl x:Class="WpfApplication5.MyUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:calcBinding="clr-namespace:CalcBinding;assembly=CalcBinding"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <!-- Uncomment the next line to see that without CalcBinding, this runs a lot faster. -->
        <TextBlock Text="{calcBinding:Binding Path=Age*2}" FontSize="1"/>
        <TextBlock Text="{Binding Path=Age}" FontSize="1"/>
    </Grid>
</UserControl>