lyrics in volta confuses Bar_engraver

[Steven McDougall]

> I'm not top posting.

\version "2.10.25"
\paper{ ragged-right=##t }

music = \relative c'
{
  \repeat volta 2 { c d e f  }
}

words = \lyricmode { c d e f }

\score
{
  \new GrandStaff
  <<
    \new Staff = upper { \new Voice = "singer" \music }

    \new Lyrics \lyricmode
    {
      \set associatedVoice = #"singer"
      \words
    }

    \new Staff = lower \music
  >>
  
  \layout
  {
    \context { \GrandStaff \accepts "Lyrics"    }

    % LilyPond manual section 7.3 Vocal music says,
    % To make lyrics avoid barlines as well, use
    \context 
    { 
      \Lyrics 
        \consists "Bar_engraver"
        \consists "Separating_line_group_engraver"
        \override BarLine #'transparent = ##t    
    }
  }
}

% The \override BarLine suppress the ':' before the bar line,
% but it still blanks out a piece of the bar line.