Maybe, I don't know, but I've read they fixed the vibrations in the JA by changing the ventral fin. Again I can't find that source, but here's a relevant forum post which references Krister Karling's book:
http://forum3.sff.n.se/viewtopic.php?f=1&t=827
I think he is only talking about the AJ here. But you can see the JA's ventral fin has been redesigned, compared to the AJ's fin.