As discussed on forums: http://community.jboss.org/message/612561
and mailing list: http://infinispan.markmail.org/thread/hixrdqas4jn5cuok

configuring such a cache needs Externalizers and optionally Key2String transformers which are bundled in the infinispan-lucene-directory module, but since this module depends on Lucene people would rather want to avoid having to move this jar to the commons lib path of the application server, but still want to configure the cache in the AS configuration to not have to start a second CacheManager.
This issue would not apply anymore if support asymmetric clusters is implemented