Could you explain why would you expect a 67 there?

Code says:
<pages index="Лялечка. Поєдинок.djvu" from=64 to=66 />
{{page break}}
<pages index="Лялечка. Поєдинок.djvu" from=2 to=2 />
<pages index="Лялечка. Поєдинок.djvu" from=69 to=69 />

so is there really a software bug, and isn't this an issue in the content itself?

<pages index="Лялечка. Поєдинок.djvu" from=69 to=69 /> should give 67 according to the current page numbering. In any case, no number is shown for this page at all.

Ah, thanks for clarifying@

uk.ws use http://en.wikisource.org/w/index.php?title=MediaWiki:PageNumbers.js not http://wikisource.org/w/index.php?title=MediaWiki:PageNumbers.js, can you switch to the later and retry ?

I have moved to the later version. It works fine.

Sounds like this was solved by using different on-wiki scripts, so -> INVALID.