Why WeakEventManager does not fire an event when the sender is not the nominal?

I don't like off-the-standard pattern, but I was making a quick test on my app, and I bumped against this strange behavior.

Consider a normal class exposing an event, here the very common PropertyChanged, but I think could be any other.

The subscriber chooses to subscribe the event via the WeakEventManager helper. Now, the "odd" thing is the actual sender reference: as long the instance is the same as was used on the subscription, everything goes fine. However, when you use another object, no notification will be issued.

Again, that's NOT a good pattern, but I wonder whether there is any good reason for this limitation, or rather that is a kind a bug. More a curiosity than a real need.

class Class1
{
    static void Main(string[] args)
    {
        var c = new MyClass();

        WeakEventManager<INotifyPropertyChanged, PropertyChangedEventArgs>.AddHandler(
            c,
            "PropertyChanged",
            Handler
            );

        c.ActualSender = c;
        c.Number = 123;  //will raise

        c.ActualSender = new Class1();
        c.Number = 456;  //won't raise

        Console.ReadKey();
    }

    static void Handler(object sender, PropertyChangedEventArgs e)
    {
        Console.WriteLine("Handled!");
    }
}

class MyClass : INotifyPropertyChanged
{
    public object ActualSender { get; set; }


    private int _number;
    public int Number
    {
        get { return this._number; }
        set
        {
            if (this._number != value)
            {
                this._number = value;
                this.OnPropertyChanged("Number");
            }
        }
    }


    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(
        string name
        )
    {
        this.PropertyChanged(
            this.ActualSender, 
            new PropertyChangedEventArgs(name)
            );
    }
}

EDIT: here is a rough way to achieve the expected behavior (hard-links for sake of simplicity).

class Class1
{
    static void Main(string[] args)
    {
        var cx = new MyClass();
        var cy = new MyClass();

        Manager.AddHandler(cx, Handler1);
        Manager.AddHandler(cx, Handler2);
        Manager.AddHandler(cy, Handler1);
        Manager.AddHandler(cy, Handler2);

        cx.ActualSender = cx;
        cx.Number = 123;

        cx.ActualSender = new Class1();
        cx.Number = 456;

        cy.ActualSender = cy;
        cy.Number = 789;

        cy.ActualSender = new Class1();
        cy.Number = 555;

        Console.ReadKey();
    }

    static void Handler1(object sender, PropertyChangedEventArgs e)
    {
        var sb = new StringBuilder();
        sb.AppendFormat("Handled1: {0}", sender);

        var c = sender as MyClass;
        if (c != null) sb.AppendFormat("; N={0}", c.Number);
        Console.WriteLine(sb.ToString());
    }

    static void Handler2(object sender, PropertyChangedEventArgs e)
    {
        var sb = new StringBuilder();
        sb.AppendFormat("Handled2: {0}", sender);

        var c = sender as MyClass;
        if (c != null) sb.AppendFormat("; N={0}", c.Number);
        Console.WriteLine(sb.ToString());
    }
}

static class Manager
{
    private static Dictionary<object, Proxy> _table = new Dictionary<object, Proxy>();

    public static void AddHandler(
        INotifyPropertyChanged source,
        PropertyChangedEventHandler handler
        )
    {
        var p = new Proxy();
        p._publicHandler = handler;
        source.PropertyChanged += p.InternalHandler;
        _table[source] = p;
    }

    class Proxy
    {
        public PropertyChangedEventHandler _publicHandler;
        public void InternalHandler(object sender, PropertyChangedEventArgs args)
        {
            this._publicHandler(sender, args);
        }
    }
}

public class PseudoEventManager : IWeakEventListener { private static PseudoEventManager _instance = new PseudoEventManager(); private readonly Dictionary<object, List<object>> _handlerTable = new Dictionary<object, List<object>>(); public bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e) { foreach (var handler in _handlerTable[sender]) // point of interest A //invoke handler } public static void AddHandler(object source, object handler) { if (!_instance._handlerTable.ContainsKey(source)) _instance._handlerTable.Add(source, new List<object>()); //point of interest B _instance._handlerTable[source].Add(handler); //attach to event } }

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