bug with tablature and pitchedTrills

[Marc Hohl]

> I am not top posting.

The snipped below shows a small note head even in the Tab Staff where a
fret number should appear.

\version "2.13.42"

noteTrills = \relative c' {
        \pitchedTrill c2\startTrillSpan d bes2\stopTrillSpan
}

\score {
  <<
  \new Staff {
    \new Voice {
      \noteTrills
    }
  }
  \new TabStaff {
    \new TabVoice {
      \noteTrills
    }
  }
  >>
}