Bizarre Kernel.exec problem caused by "dropbox" gem

demo.rb

require 'bundler/setup'
Bundler.require :default

Kernel.exec ['/bin/ls', '/bin/ls'], '-al'

description.md

bundle install, then:

$ ruby the_problem.rb 
the_problem.rb:4:in `exec': No such file or directory - -al (Errno::ENOENT)
  from the_problem.rb:4:in `<main>'

Without dropbox:

$ ruby -e "Kernel.exec ['/bin/ls', '/bin/ls'], '-al'"
total 112
drwxr-xr-x  9 rsutphin  CB\Domain Users    306 Jul 17 14:57 .
drwxr-xr-x  5 rsutphin  CB\Domain Users    170 Jul 17 14:42 ..
-rw-r--r--  1 rsutphin  CB\Domain Users     45 Jul 17 15:09 Gemfile
-rw-r--r--  1 rsutphin  CB\Domain Users    246 Jul 17 14:58 Gemfile.lock
-rw-r--r--  1 rsutphin  CB\Domain Users     92 Jul 17 15:11 the_problem.rb

(i.e., the output from ls -al.)

The ultimate culprit is this code in dropbox/extensions/array.rb:

class Array # :nodoc:
  # [...]

  def to_hash # :nodoc:
    inject({}) { |hsh, (k,v)| hsh[k] = v  ; hsh }
  end unless method_defined?(:to_hash)
end

Gemfile

source 'https://rubygems.org'

gem 'dropbox'

The 'extlib' gem will cause the same problem