NoteColumn without parents?

[Thomas Morley]

Hi,

please consider:

{
  b4\glissando
  \once \override NoteColumn.glissando-skip =
    #(lambda (grob)
      (pretty-print
        (list
          (cons 'X-parent (ly:grob-parent grob X))
          (cons 'Y-parent (ly:grob-parent grob Y))))
       #t)
  c'
  d'
}

I.e. NoteColumn seems to have no parents, at least I can't read any
parent from 'glissando-skip.
Is this on purpose?

Cheers,
  Harm