It is kind of weird when something like this changes from one firmware to another, and there isn't really a known explanation or reason. Then you add to it the context of some people having trouble with resetting amps or applying the update completely, and something like this starts to feel like it might be a bug. And if it's a bug, "turn it up" may or may not be the best advice. ;-)
It's not a bug. That amp model changed significantly from V15 to V18.
It's not a bug. That amp model changed significantly from V15 to V18.