"Bitstream Vera Sans Mono" font doesn't have Cyrillic support. "DejaVu Sans Mono" does have it and is based on the former. I suggest a patch to http://bitbucket.org/m/css/layout.css
Thanks very much for this bug report, goodrone.
We've just rolled out your fix. I'm sorry that it's taken us so long to get to it – now that we've got more hands on deck we're making an effort to stay on top of such issues.