Loading featured images results neither in error neither in visible thumbnails

I encountered the problem after upgrading from 3.6 to 3.6.1. Theme is Custom Community Free 1.17.3, I upgraded it too. After upgrade process all featured images disappeared from theme’s slideshow and posts featured image fields. I can’t even reset and re-upload them via Admin. The thumbnail of featured image doesn’t become visible, the field remains the same.
http://razvilka-45.ru