Error in resolving number of staff lines

[Marc Hohl]

Hello list,

the following snippet prints a value of 5 in both cases,
whereas the second system has
only four staff lines. What's wrong here?

Regards,

Marc

\version "2.15.41"

#(define (test-bar-print grob)
   (let* ((staff-symbol (ly:grob-object grob 'staff-symbol))
          (line-count (if (ly:grob? staff-symbol)
                          (ly:grob-property staff-symbol 'line-count)
                          0)))
          (display "\nNumber of staff lines: ")
          (display line-count)
          (ly:bar-line::print grob)))

\layout {
  \context {
    \Staff
    \override BarLine #'stencil = #test-bar-print
  }
}

\new Staff {
  s1 \bar ":|"
}

\new Staff {
  \override Staff.StaffSymbol #'line-positions = #'(-2 0 2 4)
  s1 \bar ":|"
}