Calibre > MapleRead mysterious hyphenation issue

[Pargeo]

Hello,

I came across with a very strange issue relating to the hyphenation in epub3 books that 'passed' through Calibre 6.x.

Books in question: EPUB3 books in Russian manufactured using the following algorithm: MS Word > Pages > Sigil (where cover, metadata & toc are added, plus small tweaks are made).
If I import these books directly into MapleRead, hyphenation is working ok.
But if I first import them into Calibre and then download them into MapleRead via OPDS, hyphenation stops working.
(the same books are properly hyphenated in Apple Books, whether they are imported into Apple Books directly or via Calibre + CC / Marvin etc.)

The issue doesn't appear in epub3 books in English, and it does not appear in Epub2 books at all, regardless of their language.

As far as I know, the only thing Calibre does with the books is adding a few lines to Metadata.

I understand the issue relates to Calibre only marginally, but I am in correspondence with MapleRead developer and they seem to believe it's a Calibre issue.

[kovidgoyal]

Since MapleRead is refusing to hyphenate it only MapleRead developers can tell us why it is refusing to do so. Get them to tell you that, then I can help you further.

[ShellShock]

Is this a recent problem? What version of MapleRead are you using, and have you seen the recent changelog (https://www.maplepop.com/web/mr/new_features.php#v470)?

MapleRead 4.7 (R2022.12.21)

o Support exporting notes in CSV format

o Address text hyphenation issues of some EPUB books published in a language different from the iOS system language