I'm experiencing ENFE with merge() in similar situation and noticed that https://github.com/hibernate/hibernate-orm/commit/c3819b499f6f9fd528bfd1aab05c60fddd99b1a7 was applied instead of https://github.com/zroubalik/hibernate-orm/commit/537822c9d0f0a9ca5b85903f8f80074c0de6d03f that would have dealt with this problem as well.

My problem arises through merge() operation that utilizes session.get() at DefaultMergeEventListener.entityIsDetached() which in turn is aware only of ObjectNotFoundException and not ENFE (as it should). This happens mainly because instance with assigned id was assumed to be detached and ENFE was not catched. The comment lines below state the situation as well (persistent should be transient in the last sentence, I presume).

//TODO: we should throw an exception if we really *know* for sure
//      that this is a detached instance, rather than just assuming
//throw new StaleObjectStateException(entityName, id);

// we got here because we assumed that an instance
// with an assigned id was detached, when it was
// really persistent
entityIsTransient( event, copyCache );