I received the fantastic 5.12.4. It was lurking there and as soon as I downloaded a book bought from Amazon I got caught. It is strange to remove a firmware from the official download page and release it in OTA.
I don't know what's wrong exactly with this firmware because I haven't really used it yet but in the meantime I got the cover bug (it is a bug or a "feature?")

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I hope they will update the firmware and this one is not really the latest version.