Order of the staves

[Eddy]

>Hi !

>I use the following to have a choir with a clarinet and an accordion.

\score {
  \new GrandStaff <<
    \context ChoirStaff=Choeur <<
      \context Staff=Soprano <<
        \context Voice=SopranoUn {\voiceOne \SopranoUnMusique}
        \context Voice=SopranoDeux {\voiceTwo \SopranoDeuxMusique}
      >> % end Staff Soprano
      \context Lyrics=SopranoUn {s1}
      \context Lyrics=SopranoDeux {s1}
      \context Staff=Alto <<
        \context Voice=AltoUn {\voiceOne \AltoUnMusique}
        \context Voice=AltoDeux {\voiceTwo \AltoDeuxMusique}
      >> % end Staff Alto
      \context Lyrics=AltoUn {s1}
      \context Lyrics=AltoDeux {s1}
      \context Staff=Tenor << 
        \context Voice=TenorUn {\voiceOne \TenorUnMusique}
        \context Voice=TenorDeux {\voiceTwo \TenorDeuxMusique}
      >> % end Staff Tenor
      \context Lyrics=TenorUn {s1}
      \context Lyrics=TenorDeux {s1}
      \context Staff=Basse <<
        \context Voice=BasseUn {\voiceOne \BasseUnMusique}
        \context Voice=BasseDeux {\voiceTwo \BasseDeuxMusique}
      >> % end Staff Basse
      \context Lyrics=BasseUn {s1}
      \context Lyrics=BasseDeux {s1}
      \context Lyrics=SopranoUn \lyricsto SopranoUn \SopranoUnParoles
      \context Lyrics=SopranoDeux \lyricsto SopranoDeux \SopranoDeuxParoles
      \context Lyrics=AltoUn \lyricsto AltoUn \AltoUnParoles
      \context Lyrics=AltoDeux \lyricsto AltoDeux \AltoDeuxParoles
      \context Lyrics=TenorUn \lyricsto TenorUn \TenorUnParoles
      \context Lyrics=TenorDeux \lyricsto TenorDeux \TenorDeuxParoles
      \context Lyrics=BasseUn \lyricsto BasseUn \BasseUnParoles
      \context Lyrics=BasseDeux \lyricsto BasseDeux \BasseDeuxParoles
    >> % end ChoirStaff Choeur
    \context Staff=Clarinette << 
      \ClarinetteMusique
    >> % end Staff Clarinette
    \context PianoStaff=Accordeon <<
      \context Staff=MainDroite \MainDroiteMusique
      \context Staff=MainGauche \MainGaucheMusique
    >> % end PianoStaff Accordeon
  >> % end GrandStaff
}% end score

In the pdf, the clarinet is at the top of the page ! I can't understand why it
is not after the choir ! What does control this ?
Sorry for the length of the example, I tried to cut out the unusefull lines.

I use lilpond version 2.6.4.