Subscription life cycle

What will happen if we want to stop a single observer from receiving messages from the observable event source? If we change the program Main from the preceding example to the following one, we could experience a wrong observer life cycle design. Here's the code:

//this is the message observable responsible of producing messages 
using (var observer = new ConsoleIntegerProducer()) 
//those are the message observer that consume messages 
using (var consumer1 = observer.Subscribe(new IntegerConsumer(2))) 
using (var consumer2 = observer.Subscribe(new IntegerConsumer(3))) 
{ 
    using (var consumer3 = observer.Subscribe(new IntegerConsumer(5))) 
    { 
        //internal lifecycle 
    } 
 
    observer.Wait(); 
} 
 
Console.WriteLine("END"); 
Console.ReadLine(); 

Here is the result in the output console:

The third observer unable to catch value messages

By using the using construct method, we should stop the life cycle of the consumer object. However...