error: minimise_least_squares (bug?)

[Stan Sanderson]

The following abbreviated code
% Start code sample **********
\version "2.11.23"
\include "english.ly"
\paper{ ragged-right=##t }
global = {
                \key g \major
                \clef treble
                }

upper =  \relative c''' {       
                \repeat volta 2 {
                        b4. g4 e8 ds e |                }
                \alternative {
                        {e4. e4 e8 fs g |}
                        {e4. e4 d8 cs d |}
                                }
}               

middle =  \relative c''' {
        \repeat volta 2 {
                        g,8\rest g b4 g2 |      }
        \alternative {
                {g8\rest g b4 b2\rest |}
                {g8\rest g b4 b2\rest |}
        }
}

lower =  \relative c{
        \repeat volta 2 {
                e2 ~ e2 |       }
        \alternative {
                {e2 ~ e8 r4.|}
        {e2 ~ e8 r4.|}
        }
}
        
staffClassicalGuitar = \new Staff

        {
        \time 4/4
        <<
        \new Voice = A { \voiceOne \global \upper }
        \new Voice = B { \voiceTwo \global \middle }
        \new Voice = C { \voiceFour \global \lower }
        >>
        \bar "|."
}

\score {

        <<
                \staffClassicalGuitar
        >>
                }
% End code sample *******

produces an error:
> Preprocessing graphical objects...
> programming error: minimise_least_squares ():  Nothing to minimise
> This means that vertical spacing is triggered
> before line breaking

Previous postings to the list referred to earlier versions and  
suggested a bug report...



Stan