When you compile epub3 books with kindlegen it uses the start reading location definition in the
landmarks section of the nav document (toc.xhtml) for KF8 books.
You'll need to add the following line there:
Code:
<li><a epub:type="bodymatter" href="DZIEDZICTWO-1.xhtml">Start reading</a></li>
BTW, I'd recommend setting it to DZIEDZICTWO-3.xhtml instead.