A fanout exchange is actually pub/sub. In SwiftMQ with AMQP 1.0 (or JMS) you connect your consumers to a topic and the producer sends to that topic. All consumers (= subscribers) are getting a copy of the message.
Sorry, for late response, been busy with more important things up to now. The problem was on program, which has both producer and consumer tasks. Switching those two with the places solved the problem of delivery to only one consumer.
But then, switching them back to original order resulted in proper behaviour, as expected. I frankly do not know what helped with the situation, I did not change other things in that time.
Nevertheless the thread is closed, thank you for your answer.