systemu return type differences

systemu.txt

$ cat Gemfile
source :rubygems
gem 'systemu'

$ cat wat.rb
require 'systemu'
p systemu 'ls', 'stdout' => '', 'stderr' => ''

$ rbenv shell jruby-1.6.7
$ bundle exec ruby wat.rb
[#<Process::Status: pid=58082,exited(0)>, "Gemfile\nGemfile.lock\nbin\nvendor\nwat.rb\n", ""]   # <--- systemu returns an Array instance on JRuby 1.6.7

$ rbenv shell 1.9.3-p374
$ bundle exec ruby wat.rb
#<Process::Status: pid 58184 exit 0>  # <--- systemu returns a Process instance on MRI 1.9.3