@ixtab/kbaerwald: The file attached was indeed a KF8/AZW3/mobi7/mobi8 (pick your favorite name ^^), don't be fooled by the .mobi extension
. KindleGen/KindlePreviewer generates dual .mobi files since v2, with a mobi7 part (KF8), and a legacy mobi6 part, in the same file. The mobi7 part is used on devices that supports it (Fire/PC/Mac/iOS/Android/Touch 5.1/K4 4.1), while the legacy one is used by older devices.
And, yeah, I'm pretty sure it uses another reader entierly (com.amazon.ebook.booklet.htmlreader). No idea if there's a hint of hyphenation engine in there, but it does obey the shy (soft hyphen) html entity, and supports the language detection for the dictionary.
Since my device came with 5.1, I've been mostly using mobi7 files, except for old stuff purchased on Amazon that's still in mobi6/topaz...