Hangs & doesnt read fb2

Hangs while doing "back" in browsing - stop reacting on buttons.
Doesnt understand a modern fb2 from web.
Doesnt register as fb2 file reader and another applications like FileApp doesnt know that it is possible to transfer file.fb2 to uBooks.

Reader-fb2 about uBooks: app for reading books in fb2, epub and other popular ebook formats