[Doitsu]

@slowsmile: It might be a bit difficult to spot at first glance if you don't know what to look for, but even in the epub that you generated TOC entries in the NCX TOC are missing Polish national characters.

For example, the chapter title of the first chapter is Rozdział 1. (Note the stroked L before the 1.) However this special character is missing in TOC.NCX:

    <navPoint id="navPoint-3" playOrder="3">
      <navLabel>
        <text>Rozdzia 1</text>
      </navLabel>
      <content src="Text/rozdzia_1.xhtml"/>
    </navPoint>

It should read:

    <navPoint id="navPoint-3" playOrder="3">
      <navLabel>
        <text> Rozdział 1</text>
      </navLabel>
      <content src="Text/rozdzia_1.xhtml"/>
    </navPoint>

I.e., there's a bug in the TOC generation code.

@bravosx: As a temporary fix, you could simply regenerate the TOC via CTRL+T. This should restore the missing characters since the actual headings contain them.