Today when I was messing with version 3.12 a little and received interesting error.
Quote:
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Kindle Previewer
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Enhanced Typesetting preview for this book is not supported since the Mobi file is created by an older version of Kindlegen or by 3rd party tools.<br><br>Please open the original source file directly or use the latest version of KindleGen to convert this to a compatible Mobi file.<br> <a href='https://www.amazon.com/gp/feature.html?docId=1003018611'>Learn More</a>
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OK
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I never seen this error in 3.11 and that MOBI file was created by newest KindleGen.
<speculation>
Maybe some new KindleGen version that is aware about Enhanced Typesetting is just around the corner?
</speculation>