Why does the following print ¡ÉBC¡É instead of ¡ÉBC¡É?

a.rb:
# -*- coding: utf-8 -*-

puts "bc".upcase

% ruby --version
ruby 1.9.2p180 (2011-02-18) [i386-mingw32]
% ruby -EUTF-8:UTF-8 a.rb
BC
% # ?