persisting an entity and JPA behaviour with referenced entities

[Adam Hardy]

I've got an issue with the persist operation, when I use a detached entity as 
one of the entity's referenced entities.

OpenJPA throws the
org.apache.openjpa.persistence.EntityExistsException: Attempt to persist 
detached object 
"[EMAIL PROTECTED]".

The situation is this: my MVC layer has received a new entity which it must 
create. The parent entity for this is found in a cache, in a detached state.

What I'd like to know, is why is JPA forcing me to merge this detached entity 
before allowing me to persist the new child?

It means I can't use the cache, or I have to program the DAO to merge all 
referenced entities. This latter option seems like a job that JPA should be 
doing. JPA knows this parent is a detached entity, so why can't it merge the 
managed entity?

I can't see any text in the EJB spec that would mandate this behaviour, yet 
Hibernate does it too.

Regards
Adam