When upgrading Hibernate Search from 4.2.6 to 4.3.0.Beta5 I'm getting the following error from one of our tests:

java.lang.ClassCastException: org.hibernate.action.internal.DelayedPostInsertIdentifier cannot be cast to java.lang.Comparable
at org.hibernate.internal.util.compare.ComparableComparator.compare(ComparableComparator.java:36)
at org.hibernate.type.AbstractStandardBasicType.compare(AbstractStandardBasicType.java:220)
at org.hibernate.action.internal.CollectionAction.compareTo(CollectionAction.java:172)
at org.hibernate.engine.spi.ExecutableList.add(ExecutableList.java:222)
at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:246)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushCollections(AbstractFlushingEventListener.java:265)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:103)
at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1248)
at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:412)
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.id.FlushIdGenTest.testPersistBeforeTransaction(FlushIdGenTest.java:46)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)

I'm going to include a test case in a fix proposal as pull request.