This is related to: http://www.jboss.org/community/wiki/ProblemAndClusterRPCs
All the caches associated to a CacheManager share the same underlying jgroups channel. Consider CacheManager with 2 caches associated to it: an sync repl one and an async repl one (same with dist). This new JGroups feature (see link bellow) will allow for the SYNC_REPL caches NOT to use message bundling, and for the ASYN_REPL caches to allow message bundling at the same time: i.e. using the same jgroups channel.