collection growing to 16000 and not garbage collected.

Collection Counts:

java.util.HashMap 16823 org/hibernate/engine/StatefulPersistenceContext.(org.hibernate.engine.SessionImplementor)
java.util.HashMap 16823 org/apache/commons/collections/SequencedHashMap.(int)
java.util.ArrayList 16708 org/hibernate/engine/ActionQueue.init()

StackTrace:

at org.hibernate.engine.StatefulPersistenceContext.(StatefulPersistenceContext.java:118)
at org.hibernate.impl.SessionImpl.(SessionImpl.java:209)
at org.hibernate.impl.SessionFactoryImpl.openSession(SessionFactoryImpl.java:473)
at org.hibernate.impl.SessionFactoryImpl.openSession(SessionFactoryImpl.java:497)
at org.hibernate.impl.SessionFactoryImpl.openSession(SessionFactoryImpl.java:505)
at org.jbpm.persistence.db.DbPersistenceService.getSession(DbPersistenceService.java:116)
at org.jbpm.persistence.db.DbPersistenceService.getGraphSession(DbPersistenceService.java:336)
at org.jbpm.JbpmContext.getGraphSession(JbpmContext.java:571)

Please advise any suggestions to resolve this