Another similar error I've seen when accessing a collection outside the persistence-context is this:

org.hibernate.AssertionFailure: collection owner not associated with session: no.officenet.origo.core.domain.model.person.Person.emailAddressList
        at org.hibernate.engine.internal.Collections.processDereferencedCollection(Collections.java:105)
        at org.hibernate.engine.internal.Collections.processUnreachableCollection(Collections.java:66)
        at org.hibernate.event.internal.AbstractFlushingEventListener.flushCollections(AbstractFlushingEventListener.java:245)
        at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:100)
        at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
        at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1213)
        at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:402)
        at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
        at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)
        at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:241)
        at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545)
        at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124)
        at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:266)

Then Hibernate leaks connections again becuase the same close() in AbstractPersistentCollection:243 is never executed because line 241 above throws the Exception.
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira