Being a PITA to third-party developers?
Ooops, did I say that out loud?

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Jokes aside, they unified the FW for the latest hardware platform, so it includes a lot of various stuff, which may have a wide range of effects, but as lab126 works in mysterious ways, an exhaustive list is out of the question. But basically, the full R&D run behind the latest devices (KT2 & KV).