> Due to the fact that this was for us no more than a minor specification violation and not a critical bug,
> I did not press the matter any further.
Well, this "minor specification violation" renders class trees of a depth higher than two pretty much useless, because polymorphic relations and queries are all there is to it. Given the sorry state many JPA implementations are in when it comes to entity inheritance this might not be an extreme issue, but only because huge swaths of the developer community have long given up on the concept of using entity inheritance while staying true to the JPA specification - not least because for so long Hibernate featured another "minor specification violation" that prevented discriminator values from being persisted at all by default.

Any issues related to basics like entity inheritance should in my view be top priority, because after all this is an object-oriented concept, and inheritance is clearly no minor side aspect of it. It is the whole point, the basis, the fabric. In my view, in the 4.3.x versions only the issues with caching (and randomly returning) changed entity field values top it, but such serious flaws clearly defy the usability of database technology. Save from that, flawless entity inheritance should be pretty much on top of the list of "things that are important" for any JPA implementation ...