When a kjar version is upgraded, rather than replacing existing listener, a new one is registered in Kafka server extension. 

Then, when a event is received, two process instances are started rather than one

Engineering solution

When a signal for a start node is received by the extension, and there are two deployment with the same artifcat id, the signal is just sent to the deployment id which version is the most recent one. "recent" means that 2.0 has precedence over 1.32, that 1.32 has precedence over 1.11 and 1.11 has precedence over 1.1.