Jruby 1.7 corrupts file

test.rb

#!/usr/bin/env ruby -w

require 'zlib'

in_file    = File.join('test/examples/rgb.jpg')
out_file   = 'rgb.out.jpg'
gz_file    = 'test.jpg.gz'
chunk_size = 2**16

Zlib::GzipWriter.open(gz_file) do |gz|
  File.open(in_file) do |f|
    gz.write(f.read(chunk_size)) until f.eof?
  end
end

Zlib::GzipReader.open(gz_file) do |gz|
  File.open(out_file, 'w') do |f|
    f.write(gz.read(chunk_size)) until gz.eof?
  end
end