Inconsistent interpretation of intervals in chord mode

[pls]

Hey all,

in chord mode the basic seventh step added to a tonic is the flattened seventh 
(e.g. c:1.7).  Diminished sevenths and major sevenths can be achieved by 
suffixing a '-' or '+' to the number (e.g. c:1.7- or c:1.7+).  But this 
interpretation changes when the notes extend beyond the range of one octave.  
c:1.14 is now interpreted as a major seventh, c:1.14+ and c:1.14- are now 
displayed as an augmented major seventh and a flattened seventh, respectively 
(see attachment). Currently it's not possible at all to display a diminished 
seventh one octave higher.  So this looks like a bug to me.

\version "2.19.21"

intervals = \chordmode {
  c1:1.7
  c1:1.7+
  c1:1.7-
  
  c1:1.14
  c1:1.14+
  c1:1.14-
}

<<
  \new Voice = sevenths { 
    \accidentalStyle Score.teaching
    \intervals 
  }
  \new Lyrics \lyricsto sevenths {
    "1.7"
    "1.7+"
    "1.7-"
    "1.14"
    "1.14+"
    "1.14-"
  }
>>

hth
patrick