StaleStateException when saving entity with complex relations

The hibernate entity I am saving in the database (Oracle) has very complex relations, in the sense that it has many related entities. It looks something like this...

@Table(name = "t_HOP_CommonContract")
public class Contract {
    @Id
    private ContractPK id;

    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    private ContractGroupMember contractGroupMember;

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumns({
        @JoinColumn(name = "TransactionId", referencedColumnName = "TransactionId"),
        @JoinColumn(name = "PrimaryContractId", referencedColumnName = "PrimaryContractId")
    })
    @Fetch(FetchMode.SUBSELECT)
    private List<ContractLink> contractLinks;

    // . . . . . . . 

    // A couple of more one to many relationships

    // Entity getters etc.

}

I also have a couple of more entities such as...

@Table(name = "t_HOP_TRS")
public class TotalReturnSwap {
    @Id
    private ContractPK id;
    // Entity Getters etc.
}

The trick is that I have to do persistence of Contract and TotalReturnSwap entities in the same transaction.

Sometimes it could be a bunch of entities that have to be persisted in the same transaction.

I have noticed the following exception when I save the TotalReturnSwap entity (which is always done after I have saved the Contract entity).

org.springframework.orm.hibernate3.HibernateOptimisticLockingFailureException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1; nested exception is
    org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1
    at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:675) \
    at org.springframework.orm.hibernate3.HibernateTransactionManager.convertHibernateAccessException(HibernateTransactionManager.java:793) 
    at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:664) 
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:754) 
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:723) 
    at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:147) 
    at com.rbs.fcg.publishing.DownstreamContractBusinessEventPostingService.performTDWPersistenceForContracts(DownstreamContractBusinessEventPostingService.java:102) 
    at com.rbs.fcg.publishing.DownstreamContractBusinessEventPostingService.persistContractBusinessEvent(DownstreamContractBusinessEventPostingService.java:87)
    at com.rbs.fcg.publishing.DownstreamContractBusinessEventPostingService.publish(DownstreamContractBusinessEventPostingService.java:67)
    at com.rbs.fcg.publishing.PublishingProcessor.publish(PublishingProcessor.java:76)
    at com.rbs.fcg.publishing.PublishingProcessor.process(PublishingProcessor.java:52)
    at com.rbs.are.MultiThreadedQueueItemProcessor$2.run(MultiThreadedQueueItemProcessor.java:106)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1
    at org.hibernate.jdbc.Expectations$BasicExpectation.checkBatched(Expectations.java:85)
    at org.hibernate.jdbc.Expectations$BasicExpectation.verifyOutcome(Expectations.java:70)

Now a few points that may help while answering questions:

• I am only saving (inserting) entities in database - never updating/ deleting/ reading
• I have been able to isolate this exception even in single threaded environments, so it does not look like a multi-threading, issue even though our application is multi-threaded