Creating multiple instances of a mock object

I modified the Publisher/Subscriber example to reject duplicate subscriber instances.  It ran and passed the test that I had created. I then added the following test to show that three different subscribers would each receive the message once, when piblished:

        @Test
        public void testPublish3()
        {
                // Set up test.
                final Publisher publisher = new Publisher();
                final Subscriber subscriber1 = context.mock(Subscriber.class);
                final Subscriber subscriber2 = context.mock(Subscriber.class);
                final Subscriber subscriber3 = context.mock(Subscriber.class);
                publisher.add(subscriber1);
                publisher.add(subscriber2);
                publisher.add(subscriber3);
                final String message = "message";

                // Set up expectations.
                context.checking(new Expectations() {{
                        exactly(1).of(subscriber1).receive(message);
                        exactly(1).of(subscriber2).receive(message);
                        exactly(1).of(subscriber3).receive(message);
                }});

                // Execute action.
                publisher.publish(message);

                // Verify results.
                context.assertIsSatisfied();
        }

This compiles fine but the test crashed with the following error:

java.lang.IllegalArgumentException: a mock with name subscriber already exists
        at org.jmock.Mockery.mock(Mockery.java:128)
        at org.jmock.Mockery.mock(Mockery.java:120)
        at jmock.PublisherTest.testPublish3(PublisherTest.java:61)  (i.e. where subscriber2 is declared, above).

How should I have written this test?

Thanks,
Vince.