What are the semantics according to this specification, if includeAllAttributes is set to false (like in my example above)?

According to the spec you can set attributes which JPA provider must load. But you can't set attributes which JPA provider must not load. So if you set includeAllAttributes to false that Hibernate is free to load all or load nothing (according to the spec).

P.S. It is how I underestand the spec and current implementation. Hibernate guys may have their own opinion.