This needs to be further investigated to analyze why the strategy changed.
Merely documenting that behavior has changed is not only insufficient, it may even be root of certain errors that will surface out downstream. Such errors can be hard to relate with this root cause..
That is what the document says:
"The FieldMapping.getStrategy() in OpenJPA 1.x returned an instance of RelationFieldStrategy for embded super classes, but will now return an EmbedFieldStrategy. "
Here is the test that records this unexplained change in behavior.
the definition of the field 'sup' in EmbeddableSuperSub
public class EmbeddableSuperSub extends EmbeddableSuper
private EmbeddableSuper sup;
where EmbeddableSuper is a MappedSuperclass.
Firstly the names of the test classes are misleading because MappedSuperClass has nothing to do with being embeddable.
Secondly there is no apparent explanation on why suddenly a many-to-one relation to a MappedSuperClass that used to be RelationFieldStrategy will now handled by a EmbedFieldStrategy
My hypothesis is this issue is related to some other decisions we were making around embeddablity of a type.
I am reopening to investigate further.