Do you mean their state does synchronize after the merge? This is the responsibility of the application (JGroups has no way of knowing what the state is, whether it should be merged, or how to merge it). If you implement the JGroups MembershipListener interface you can be notified of changes in the group membership.
You need to
- add pbcast.STATE_TRANSFER to the top and
- enable automatic fetching of state after reconnect: Channel.setOpt(Channel.AUTO_GETSTATE, Boolean.TRUE)