[ruby-core:33162] Windows Unicode (chcp 65001) Generates incorrect output

Hello,

While working on solving the ANSI coloring issue for application, we
spotted a possible encoding issue of STDOUT/ERR puts and print

The following script, saved as UTF-8 and with magical encoding headers
of utf-8 will attempt to convert it's content to the default external
encoding.

===
# encoding: utf-8

puts "__ENCODING__: #{__ENCODING__}"
puts "Encoding.default_external: #{Encoding.default_external}"

line = "Ésta es una línea"
encoded = line.encode(Encoding.default_external)

puts "line.size: #{line.size}"
puts "encoded.size: #{encoded.size}"
puts "line.bytesize: #{line.bytesize}"
puts "encoded.bytesize: #{encoded.bytesize}"

puts line
puts encoded

print line, "\n"
print encoded, "\n"

line.chars.each { |c| print c }; print "\n"
encoded.chars.each { |c| print c }; print "\n"

===

This script, when run on "chcp 1252" generates the following output:

>ruby -v encoding-output.rb
ruby 1.9.3dev (2010-11-14 trunk 29779) [i386-mingw32]
__ENCODING__: UTF-8
Encoding.default_external: Windows-1252
line.size: 17
encoded.size: 17
line.bytesize: 19
encoded.bytesize: 17
Ésta es una línea
Ésta es una línea
Ésta es una línea
Ésta es una línea
Ésta es una línea
Ésta es una línea

Which is expected, line needs to be encoded to default_external for
proper output (encoded).

Now, testing against chcp 65001 (Unicode UTF-8) we obtain an undesired result:

>ruby -v encoding-output.rb
ruby 1.9.3dev (2010-11-14 trunk 29779) [i386-mingw32]
__ENCODING__: UTF-8
Encoding.default_external: UTF-8
line.size: 17
encoded.size: 17
line.bytesize: 19
encoded.bytesize: 19
Ésta es una líneaea
Ésta es una líneaea
Ésta es una líneaea
Ésta es una líneaea
É�sta es una lí�nea
É�sta es una lí�nea

Please note that both line and encoded are printed correctly, but
extra characters are added. Also, when performing "chars" enumeration,
the output of both line and encoded are incorrect.

I was wondering if someone is aware of this issue.

Please excuse my naive approach to this encoding problem and thanks in
advance for any hint on proper testing.

Thank you.
-- 
Luis Lavena
AREA 17
-
Perfection in design is achieved not when there is nothing more to add,
but rather when there is nothing more to take away.
Antoine de Saint-Exupéry