Originally Posted by Perkin
There's a bug in QT (no fault of Sigil) that has problems with bold/italics when used with embedded fonts.
If you're using an embedded font with it's variations bold/italic then the previewer built in to sigil (and calibre) can't show them properly, that may be why they show correctly when you assign a system font.
Thank you Perkin!
I used embedded fonts in the ePub and by removing all entries from style sheet and content.opf/manifest, Sigil render text properly (Times New Roman is one of my system fonts).
But now ADE shows me "?" instead of characters.
P.S. I found the answer - ADE doesn't support Cyrillic letters. So the only solution at the moment is to keep embedded fonts in the ePub file.