Stanza is displaying at bottom of score

[Jethro Van Thuyne]

In the following minimal example, a repeated stanza is showing up
under the PianoStaff. Of course, I would need it to be under the
first stanza, above the PianoStaff. Am I missing some setting,
how can I fix this? Any help much appreciated :)

Kind regards,

Jethro

Screenshot: 
http://jethro.be/upload/sc_stanzas.png

Minimal example:
\version "2.17.24"
\score {
  <<
    \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.
        }
      >>
    }
    \new PianoStaff
    {
      << { a b c d c d e f } { a b c c c d e f } >>
    }
  >>
}