Chord substitution mystery

[Stan Mulder]

I was using a chord substitution scheme submitted here by Kieren MacMillan. It
works well and I enhanced it for augmented chords. However, I'm trying to
display a plus sign as the augmented symbol and in the case of the C augmented7
chord it displays C7/#5 instead of C+7. Whereas the C aug 9 is fine, showing
C+9:

 \paper {
   ragged-last  = ##f
 }
 
 \include "english.ly"
 
 FGGChordNames =
 {
         <c e g b d'>1-\markup { \super "maj9" }
         <c e g a d'>1-\markup { \super "6(add9)" }
         <c e gsharp'>1-\markup { + }
         <c e gsharp bflat'>1-\markup { +\super "7" }
         <c e gsharp bflat d'>1-\markup { +\super "9" }
 }
 chExceptions = #(append (sequential-music-to-chord-exceptions 
      FGGChordNames #t) ignatzekExceptions)
 
 melody = \relative c'' {
        c4 c c c c
        \bar "|."
 }
 
 harmonies = \chordmode {
        \set chordChanges = ##f
        \set chordNameExceptions = #chExceptions
        c4:maj9
        c4:6.9
        c4:aug
        c4:aug7
        c4:aug9
 }
          
 \score {
        &lt:&lt;
                \new ChordNames {
                        \set chordChanges = ##t
                        \harmonies
                }
                \new Voice = "one" {
                        \melody
                }
         &gt:&gt;
         \layout { }
         \midi { }
 }