lilypond 2.1.28 : alterations don't show up with \harmonic.

[Alexandre Beneteau]

Hello,

The following lilypond code will show the problem :

\score {
  \notes
  \relative c' {
  <c g'\harmonic>
  <cis gis'\harmonic>
  }
}

cis is well displayed, but there is no difference between g'\harmonic and 
gis'\harmonic.

TIA,

        Alexandre.