Strange bug - Register 2 methods with a different signature to event

Question

I've found strange behavior in C#.

Look at the example below:

namespace ConsoleApplication1
{
    class MyClass
    {
        public event Action<MyClass> Event;
        public void OnEvent(MyClass arg) { }
        public void OnEventObject(object arg) { }
    }

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                MyClass myClass = new MyClass();
                myClass.Event += (Action<object>)myClass.OnEventObject; // Succeed.
                myClass.Event += myClass.OnEvent; // ArgumentException: Delegates must be of the same type.
            }
            catch { Console.WriteLine("Section 1 failed!"); }

            try
            {
                MyClass myClass = new MyClass();
                myClass.Event += myClass.OnEvent; // Succeed.
                myClass.Event += (Action<object>)myClass.OnEventObject; // ArgumentException: Delegates must be of the same type.
            }
            catch { Console.WriteLine("Section 2 failed!"); }

            try
            {
                MyClass myClass = new MyClass();
                myClass.Event += myClass.OnEvent; // Succeed.
                myClass.Event += myClass.OnEventObject; // Succeed.
            }
            catch { Console.WriteLine("Section 3 failed!"); }

            try
            {
                MyClass myClass = new MyClass();
                myClass.Event += myClass.OnEventObject; // Succeed.
                myClass.Event += myClass.OnEvent; // Succeed.
            }
            catch { Console.WriteLine("Section 4 failed!"); }
        }
    }
}

Section 1 and 2 Failed on the last Registration.

Section 2 and 3 Succeed.

Why does it happen?

I think the first section Is severe bug! Because the last registration event failed despite the signing method is compatible with hundred percent!