Lilypond generates a chord from nowhere

[Stan Mulder]

I have a fretboard problem.

I have defined a new fretboard for a plectrum banjo. Everything is working
properly when I specify a chord, except when I specify a SLASH chord, i.e.,
a chord with a designation for the bass player. So for example, if I specify
a G half-diminished chord, all is well. But if I specify a G half-diminished
chord with a D-flat in the bass, I get a fretboard fingering I don't recognize.

Okay: g:m7.5-
Not okay: g:m7.5-/dflat

Basically, I think the chord in both instances (with or without the slash
notes) should be exactly the same fingerings. How can I correct this?

Here's an example below:


\version "2.19.15"
\include "english.ly"

%% tunings for 4-string banjo
\makeDefaultStringTuning #'plectrumTuning \stringTuning <c g b d'>

\storePredefinedDiagram #default-fret-table \chordmode {c}           
#plectrumTuning  #"o;o;1;2;" % C
\storePredefinedDiagram #default-fret-table \chordmode {g:m7.5-}     
#plectrumTuning  #"5;3;2;5;" % Gø

chordNames = \chordmode {
        c1 g:m7.5- g:m7.5-/dflat
        
}

melody = \relative c'' {
        c1 c c
}

\score {
        <<
                \new ChordNames \chordNames
                \new FretBoards \chordNames { 
                                \set Staff.stringTunings = #plectrumTuning
                                \override 
FretBoard.fret-diagram-details.finger-code = #'in-dot
                                \override 
FretBoard.fret-diagram-details.number-type = #'arabic
                }
                \new Staff { \melody }
        >>
}





%Stan