lsof vs ruby's IO#closed?

_mri_1.8_results

$ ruby -v
ruby 1.8.7 (2012-02-08 patchlevel 358) [i686-darwin13.4.0]

# then we execute "ruby close_and_redirect.rb", and lsof at select points
# (see the two ruby scripts in this gist) during execution:

$ lsof -p 10623
COMMAND   PID   USER   FD   TYPE DEVICE  SIZE/OFF     NODE NAME
ruby    10623 Sophia    0u   CHR   16,3    0t1427      663 /dev/ttys003
ruby    10623 Sophia    1u   CHR   16,3    0t1427      663 /dev/ttys003
ruby    10623 Sophia    2u   CHR   16,3    0t1427      663 /dev/ttys003
# during the above, ruby reports "STDOUT closed?: false" ...ok

$ lsof -p 10623
COMMAND   PID   USER   FD   TYPE DEVICE  SIZE/OFF     NODE NAME
ruby    10623 Sophia    0u   CHR   16,3    0t1478      663 /dev/ttys003
ruby    10623 Sophia    2u   CHR   16,3    0t1478      663 /dev/ttys003
# during the above, ruby reports "STDOUT closed?: true" ...ok

$ lsof -p 10623
COMMAND   PID   USER   FD   TYPE DEVICE  SIZE/OFF     NODE NAME
ruby    10623 Sophia    0u   CHR   16,3    0t1530      663 /dev/ttys003
ruby    10623 Sophia    2u   CHR   16,3    0t1530      663 /dev/ttys003
# during the above, ruby reports "STDOUT closed?: false" !!

close_and_redirect.rb

STDERR.puts "STDOUT closed?: #{STDOUT.closed?}"
STDERR.puts "sleeping... try lsof -p #{$$}\n"
sleep 10

STDOUT.close
STDERR.puts "STDOUT closed?: #{STDOUT.closed?}"
STDERR.puts "sleeping... try lsof -p #{$$}\n"
sleep 10

exec "ruby", "test_stdout.rb"

test_stdout.rb

STDERR.puts "STDOUT closed?: #{STDOUT.closed?}"
STDERR.puts "sleeping... try lsof -p #{$$}"
sleep 10

puts "STDOUT says hello"