lyrics placement with two voice

[Manfred Sherlock Olm]

with this example as small as possible ;-)

\version "2.10.20"
\header {
        title = "Hymne à la nuit (extrait pour report de bogue)"
        filename = "hymneNuit.ly"
}

soprano = {
        \clef treble
        \key c\minor
        \time 3/4
        ees'4 aes'4. g'16 (f'16)                % mesure 19
        g'4 f'2                                 % mesure 20
        ees'2 bes'4                             % mesure 21
}

alto =  {
        \clef treble
        \key c\minor
        \time 3/4
        d'8 (c'8) c'8 (b8) c'4                          % mesure 19
        ees'2 d'4                                       % mesure 20
        ees'2 ees'4                                     % mesure 21
}


coupletUn =  \lyrics{
 mant tout en rêve heu- reux.
}

\score {
        \new ChoirStaff <<
                \new Voice = "sopPortee" { \soprano }
                \new Lyrics \lyricsto "sopPortee" { \coupletUn }
                \new Voice = "altPortee" { \alto }
                \new Lyrics \lyricsto "altPortee" { \coupletUn }
        >>
}

there are 2 issues :

* the place in second voice of "en" over "tout"
* the place in second voice of "heu" not under the note

I dont understand why

Regards and thank's a lot for this beautiful software

Manfred Serlock Olm