Thanks! I didn't know about this editor, I was looking at the files..

But in the editor, the ToC file of the epub looks fine..
Now I see, there are multiple entries to the same file, but different location inside it. Is it forbidden for kepubs?
OK! I've managed it. Works perfect. So now I'm checking ToC with editor for every book and simply sending epub with KoboTouchExtended. I have last question though: options Replace Content Language Code, Clean up ePub Markup and Hyphenate Files should be ticked? They are by default on with Kepub Output and off with KoboTouchExtended.