使用孤儿院清除触发约束违反Hibernate

I'm having trouble with a JPA/Hibernate (3.5.3) setup, where I have an entity, an "Account" class, which has a list of child entities, "Contact" instances. I'm trying to be able to add/remove instances of Contact into a List<Contact> property of Account.I'm having trouble with a JPA/Hibernate (3.5.3)