I want to be able to retrieve the existing version of an entity so I can compare it with the latest version. E.g. Editing a file, I want to know if the value has changed sin
It's a normal behavior.
Doctrine stores a reference of the retrieved entities in the EntityManager so it can return an entity by it's id without performing another query.
You can do something like :
$entityManager = $this->get('doctrine')->getEntityManager();
$repository = $entityManager->getRepository('KnowledgeShareBundle:Post');
$post = $repository->find(1);
$entityManager->detach($post);
// as the previously loaded post was detached, it loads a new one
$existingPost = $repository->find(1);
But be aware of that as the $post entity was detached, you must use the ->merge() method if you want to persist it again.