title: ConcurrentModificationException upon committing transaction with Hibernate
body: <p>In our application we have upgraded from Hibernate 3.5.6-final to 4.2.21.Final and now we are getting a <code>ConcurrentModificationException</code> when a database transaction is committed:</p>
  
  <pre><code>java.util.ConcurrentModificationException: null
      at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
      at java.util.ArrayList$Itr.next(ArrayList.java:851)
      at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:386)
      at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:304)
      at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:349)
      at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:56)
      at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1195)
      at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:404)
      at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
      at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)
  </code></pre>
  
  <p>Is this a known issue with Hibernate 4.2?</p>