Deliver the events to the DiscoveryListener async to the mutlicast/heartbeating thread so that that if the DiscoveryListener blocks for while (like if he is being debuged) then we don't erroniously assume that memebrs int the group have timed out.
incubator/activemq/trunk/activemq-core/src/main/java/org/apache/activemq/transport/discovery/multicast/MulticastDiscoveryAgent.java