EPUB export converts non-breaking hyphens to regular hyphens. This behavior should be corrected immediately and export a non-breaking hyphen in an InDesign document to a "& # 8209 ;" HTML glyph.

This glyph, when inserted into an EPUB XHTML content file via manual editing, is respected by most EPUB readers including Thorium. There is thus no standards-based reason to convert these on export.