Cyrillic chars in headers become empty while defining headers ids.

"Мир", "Труд", "Май" -----> "", "-1", "-2" . The first header with empty id is ignored in TOC

I've made some edits for myself:
yuriykashin@e0a712d, js in ohthejoy: yuriykashin@3936a81
Not sure whether to pull request, maybe the problem is a little wider than only cyrillic stuff