\transposition + partcombine + midi

[Mark Pim]

> I'm not top posting.

Summary
-------
When \set Staff.midiInstrument comes before \transposition in music that is fed
into \partcombine, the top staff of the score has that transposition applied to
it in the MIDI output only. PDF output is as expected.

Demo
----

\version "2.10.33"

\paper{ ragged-right=##t }

untransposed = \relative c'' {
        \key c \major
        \set Staff.midiInstrument = "flute"
        
        R1
        c4 c d d
}

transposed = \relative c'' {
        % Putting this midiInstrument command BEFORE the \transposition
        % causes the flute part above to be transposed
        % in the MIDI output (but not in the PDF output)
        \set Staff.midiInstrument = "trumpet"
        \transposition bes
        \key d \major

        R1*2
}

\score {
        <<
                        \new Staff \untransposed
                        \new Staff \partcombine \transposed \transposed
        >>
        \layout{ }
        \midi{ }
}