Missing notes after lyrics end: bug?

[Arjen Bax]

I am typesetting an SATB hymn with where the lyrics of the four voices
are almost the same. This results in ChoirStaff setup with two Staff
contexts and a Lyrics context inbetween. The staff contexts each contain
two voices.

  \new ChoirStaff <<
    \new Staff = upper <<
      \new Voice = sop
      \new Voice = alt
    >>
    \new Lyrics \lyricsto alt
    \new Staff = lower <<
      \new Voice = ten
      \new Voice = bas
    >>
  >>

Now in bar 38 soprano and bass have 2 syllables less than alto and
tenor. I'd like to add the alternative soprano text above the upper
staff just for that single bar.

I have tried the following, defining the auxiliary soparno lyrics to be:

  sopTxt = \new Lyrics = sopL \with {
    alignAboveContext = "upper"
  }
  \lyricsto sop \lyricmode { be with Him }

and replacing bar 38 of the soprano melody { c4 g g2 } by

  << { c4 g g2 } { \sopTxt } >>

This has the intended effect of the lyrics "be with Him" being aligned
above the upper staff, but as a side effect, the complete soprano melody
from the next bar onwards vanishes! Is this a bug, or should I do this
differently?

Complete minimal working example, omitting the lower staff:

  \version "2.16.2"

  sopTxt = \new Lyrics = sopL \with { alignAboveContext = "upper" }
    \lyricsto sop \lyricmode { A C }

  sopV = \relative c'' { << { c2 c } { \sopTxt } >> c4 c c c }
  altV = \relative c'  { c4 c c c c c c c }

  \score {
    \new ChoirStaff <<
      \new Staff = upper <<
        \new Voice = sop { \voiceOne \sopV }
        \new Voice = alt { \voiceTwo \altV }
      >>
      \new Lyrics \lyricsto alt { A B C D E F G H }
    >>
  }

Where are the four c4 notes of the soprano?

Vriendelijke groet / Kind regards / Vennlig hilsen,
Arjen Bax