glissando not displayed in Staff

[Federico Bruni]

Hi,

do you know why glissando is not displayed in the Staff of the following 
snippet?
It's displayed only if I move down one octave, i.e. \relative c


\version "2.15.38"

\paper {
  ragged-right = ##f
}


music =  \relative c' {
  s1*2
  <b g'>8 e4 d4( \glissando dis8) e4 |
}

\score {
  \new StaffGroup <<
    \new Staff <<
      \context Voice { \clef "G_8" \voiceOne \music }
    >>
    \new TabStaff  <<
      \context TabVoice { \clef "moderntab" \voiceOne \music }
    >>
  >>
}