NreDemo.cs

public class NreDemo : INotifyPropertyChanged
{
    private int _value;
    private int _count;
    public event PropertyChangedEventHandler PropertyChanged;

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

    [Test]
    public async Task NreTest()
    {
        PropertyChanged += OnPropertyChanged;
        string s = null;
        var mre = new ManualResetEvent(false);
        Task.Run(() =>
        {
            try
            {
                Value = 2;
            }
            catch (Exception e)
            {
                s = e.Message;
            }
            finally
            {
                mre.Set();
            }

        });
        await Task.Delay(200);
        PropertyChanged -= OnPropertyChanged;
        mre.WaitOne();
        Assert.AreEqual("Object reference not set to an instance of an object.", s);
    }

    private void OnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
    {
        _count++;
    }

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        if (PropertyChanged != null)
        {
            Thread.Sleep(500);
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

NreDemoloop.cs

public class NreDemoloop : INotifyPropertyChanged
{
    private int _value;
    private int _count1;
    private int _count2;
    public event PropertyChangedEventHandler PropertyChanged;

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

    [Test]
    public void NreTest()
    {
        var ints = new List<Tuple<int,int>>();
        for (int i = 0; i < 1000; i++)
        {
            _count1 = 0;
            _count2 = 0;
            bool noException = true;
            string s = null;
            var mre = new ManualResetEvent(false);
            Task.Run(() =>
            {
                while (noException)
                {
                    try
                    {
                        Value = _count1;
                        _count1++;
                        Thread.Sleep(1); // Adding this sleep makes the nre happen more often, why?
                    }
                    catch (Exception e)
                    {
                        ints.Add(Tuple.Create( _count1,_count2));
                        //ints[i] = _count1;
                        noException = false;
                        mre.Set();
                    }
                }
            });
            Task.Run(() =>
            {

                while (noException)
                {
                    PropertyChanged += OnPropertyChanged;
                    PropertyChanged -= OnPropertyChanged;
                    _count2++;
                }
            });
            mre.WaitOne();
        }


        //Console.WriteLine(string.Join(", ", ints));
        var ones = ints.Select(x => x.Item1).Average();
        var twos = ints.Select(x => x.Item2).Average();
        Console.WriteLine(string.Format("n: {0} average: {1} count1: {2} count2: {3}", ints.Count, ones,ones,twos)); // n: 1000 average:214,071
    }

    private void OnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
    {
    }

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