Starting many process with human tasks via JMS ends in: Could not commit session: java.lang.NullPointerException

Starting many process with human tasks via JMS ends in: Could not commit session: java.lang.NullPointerException.

14:16:13,966 WARN [org.drools.persistence.SingleSessionCommandService] (Thread-7 (HornetQ-client-global-threads-1162166649)) Could not commit session: java.lang.NullPointerException

To reproduce:
1.) Download BPMS 6 ER2 and merge it with JBoss EAP 6.1.
2.) Setup user guest, with password guest. Hint:
guest=b5d048a237bfd2874b6928e1f37ee15e
guest=kie-user,ADMIN
3.) Configure both business-central.war and dashbuilder.war to use MySQL database. Add mysql-connector-java-5.1.26-bin.jar and mysql-ds.xml to ${EAP_DIR}/standalone/deployments to deploy a MySQL datasource. Change DS name to java:jboss/datasources/mysqlDS and hibernate dialect to org.hibernate.dialect.MySQL5InnoDBDialect in dashbuilder.war/WEB-INF/jboss-web.xml and business-central.war/WEB-INF/classes/META-INF/persistence.xml.
4.) Add role kie-user to JMS configuration in standalone.xml, subsystem messaging -> security settings to enable guest user to send messages to JMS queues.
5.) Run it with
cd ${EAP_DIR}/bin
./standalone.sh
6.) Install PerfCake 1.0-SNAPSHOT
git clone https://github.com/PerfCake/PerfCake.git
cd PerfCake
git checkout devel
mvn clean install -DskipTests
7.) Run perf scenario, just two iterations are enough to break:
git clone git://git.app.eng.bos.redhat.com/jbossqe-process-flood.git
cd jbossqe-process-flood/bpms-6.x
./execute_scenario.sh -Dscenario=HumanTask_startProcess_JMS

My environment:
BPMS 6 ER2
JBoss EAP 6.1
MySQL 5.5.32
mysql-connector-java-5.1.26-bin.jar driver