Problem with lyrics with repeat [lilypond 2.13.63]

[Raphael Manfredi]

Hello,

I'm having problems formatting lyrics on a repeat section.
I've extended the snippet from the documentation to add 2 voices
to the chorus, and the lyrics for the second stanza are moved
at the bottom of the group.

Vertically, I have:

        Soprano staff
        Lyrics for soprano #1

        Alto staff
        Lyrics for alto #1

        Lyrics for soprano #2
        Lyrics for alto #2

I'd thought it would come up as:

        Soprano staff
        Lyrics for soprano #1
        Lyrics for soprano #2

        Alto staff
        Lyrics for alto #1
        Lyrics for alto #2

in the repeated section.

Here's the modified snippet.  How should I change the example to
get the above layout?

\score {
\new ChoirStaff  <<
    \new Staff {
      \new Voice = "melody" {
        \relative c'' {
          a4 a a a
          \repeat volta 2 { b4 b b b }
        }
      }
    }
    \new Lyrics \lyricsto "melody" {
      Not re -- peat -- ed.
      <<
        { The first time words. }
        \new Lyrics {
          \set associatedVoice = "melody"
          Sec -- ond time words#one.
        }
      >>
    }
    \new Staff {
      \new Voice = "melody2" {
        \relative c'' {
          a4 a a a
          \repeat volta 2 { b4 b b b }
        }
      }
    }
    \new Lyrics \lyricsto "melody2" {
      Not re -- peat -- ed.
      <<
        { The first time words. }
        \new Lyrics {
          \set associatedVoice = "melody2"
          Sec -- ond time words#two.
        }
      >>
    }
  >>
}

Thanks,
Raphael