WPF backwards compatibility issue

gistfile1.cs

namespace WpfApplication1
{
	using System;
	using System.ComponentModel;
	using System.Diagnostics;
	using System.Globalization;
	using System.Runtime.CompilerServices;
	using System.Windows;
	using System.Windows.Data;

	using WpfApplication1.Annotations;

	/// <summary>
	/// Interaction logic for MainWindow.xaml
	/// </summary>
	public partial class MainWindow : Window
	{
		public MainWindow()
		{
			InitializeComponent();
			DataContext = new ViewModel();
		}
	}

	public class ViewModel : INotifyPropertyChanged
	{
		private string _value;

		public string Value
		{
			get
			{
				return _value;
			}
			set
			{
				if (value == _value)
				{
					return;
				}
				_value = value;
				OnPropertyChanged();
			}
		}

		public event PropertyChangedEventHandler PropertyChanged;

		[NotifyPropertyChangedInvocator]
		protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
		{
			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
		}
	}

	public class Converter : IValueConverter
	{
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
			Debug.Print($"Convert value: {value}, parameter: {parameter}");
			return value;
		}

		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			Debug.Print($"ConvertBack value: {value}, parameter: {parameter}");
			return value;
		}
	}
}

gistfile2.xml

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication1"
        mc:Ignorable="d"
		d:DataContext="{d:DesignInstance local:ViewModel}"
        Title="MainWindow" Height="350" Width="525">
	<Window.Resources>
		<ResourceDictionary>
			<local:Converter x:Key="Conv" />
		</ResourceDictionary>
	</Window.Resources>
    <StackPanel>
        <TextBox Text="{Binding Value, Converter={StaticResource Conv},
			ConverterParameter='param', UpdateSourceTrigger=LostFocus}" />
		<TextBox />
    </StackPanel>
</Window>