Re: Issue 645 in lilypond: midiInstrument + \transposition + \partcombine = wrong MIDI output

[lilypond]

Comment #1 on issue 645 by address@hidden: midiInstrument +  
\transposition + \partcombine = wrong MIDI output
http://code.google.com/p/lilypond/issues/detail?id=645

While testing a template, which I hoped would avoid such issues, I happened  
to find that midiInstrument is not an essential ingredient.

% A \transposition event while voices are 'a duo' in \partcombine
%  can leak into the previous MIDI channel
\score {
  <<
    \new Staff {
      \key c \major
      c'' c'' % Midi output, from 2.12.3 or 2.13.35, is c'' bes'
    }
    \new Staff {
      \key d \major
      \transposition bes
      \partcombine
      {
        a'
        \transposition bes
        d'
      } {
        d'
        d'
      }
    }
  >>
  \layout{ }
  \midi{ }
}