The tests prove that when core-size=0 the reject exceptions are thrown for the threads that exceed the maxThreadPoolSize. : https://github.com/jboss-set/eap-additional-testsuite/commit/5a26ceff80d26e4a04cb8285def9335da6985a20
https://github.com/jboss-set/eap-additional-testsuite/commit/280cc04e48197a30b39572ee86ab9f86dec85580