Thank you for your hints! In fact, I'm not
thus keen on rendering my epubs as kepubs. there are advantages of the kepub mode - there are people who don't even like them, though - but there are also some problems that normally leave me to remain at the epub format. For example the hyphenation feature of Kobo doesn't work - at least for me, very reliable, there are many errors, whereas the epub-plugin of
SauliusP (Calibre) is very good.
It was mere curiosity that lead me to test the new plugin.