repeats and lyrics

[Russ Ross]

I'm a bit confused about how to use repeats with lyrics.  I've
included a snippet from a chorale below.  As is, it gives one warning
and points to part of the repeat statement in the lyrics:

  warning: no one to print a repeat brace:
    \repeat fold 2 {
                     } \alternative {

but the output is as I expected, namely:

notes | notes :| more notes
words  one       unrepeated words
words  two

When I uncomment the lines to include the alto line, I get the same
warning (twice this time) and a bunch of junked lyric event warnings. 
The result is the same for the soprano line, but the alto line on gets
the first verse before the repeat (but correctly continues after the
repeat).

Can anyone lend me a bit of insight as to what I'm doing wrong?  I'd
like to understand (and correct) the warning as well as get the second
line of alto lyrics printing correctly (the tenor and bass lines
suffer from the same problem).  Supplying different notes and lyrics
for the alto doesn't help, i.e., the problem doesn't seem to be
related to my re-use of the same notes and lyrics in this example.

Thanks,

Russ

%%%%%%%%%%%%%%%%%%%
\version "2.2.0"

sopranoNotes = \notes \relative c'' {
  \repeat volta 2 {
    gis4 | cis b a gis | fis2 gis4\fermata
    dis' | e e dis8[ cis] dis4 | cis2.\fermata
  }
  e4 | dis8[ cis] b4 cis dis | e2 e4\fermata
}

sopranoLyrics = \lyrics {
  \repeat fold 2 { } \alternative {
    {
      Er -- ken -- ne mich, mein H\"u -- ter,
      mein Hir -- te, nimm mich an,
    }
    {
      Von dir, Quell al -- ler G\"u -- ter,
      ist mir viel Gut's ge -- than.
    }
  }
  Dein Mund hat mich ge -- la -- bet
}

\score {
  \new StaffGroup \simultaneous {
    \context Staff = sopranoStaff \notes
    \context Voice = sopranoVoice {
      \time 4/4 \partial 4
      \key e \major
      \autoBeamOff
      \sopranoNotes
    }
    \lyricsto sopranoVoice \new Lyrics \sopranoLyrics
%    \context Staff = altoStaff \notes
%    \context Voice = altoVoice {
%      \time 4/4 \partial 4
%      \key e \major
%      \autoBeamOff
%      \sopranoNotes
%    }
%    \lyricsto altoVoice \new Lyrics \sopranoLyrics
  }

  \paper {}
}