save() is supposed to take a transient instance as argument, and not a persistent instance. The javadoc is not very exhaustive, but AFAIK, calling save() on a persistent instance has no effect, other than cascading the operation to transient instances attached to the entity, is such a cascade is configured.
Note that there is usually no reason to call save() or saveOrUpdate() on an attached, persistent entity, since Hibernate dirty-checks the entities and makes persists the changes automatically.
