Ruby Regexp match named capture

regexp.rb

# Regex with two named captures both named "word"
r = %r{
  (?<word>[a-z]+)\s+
  (?<word>[a-z]+)
}xi

m = r.match("one two")
# => #<MatchData "one two" word:"one" word:"two">

m.captures
# => ["one", "two"]

m[:word]
# => "two"

#
# Where is [:word] "one"?
#
# It's visible in the MatchData captures.
# Shouldn't [:word] be enumerable if there is more than one?
#

#
# Further, the \g<name> construct should reuse previous groups:
# http://www.ruby-doc.org/core-1.9.3/Regexp.html#label-Subexpression+Calls
#
# My understanding is that this should be the same as above, but this time it drops "one" altogether:
#

r = %r{
  (?<word>[a-z]+)\s+
  \g<word>
}xi

m = r.match("one two")
# => #<MatchData "one two" word:"two">

m.captures
# => ["two"]