piano staff curly brackets too big

[Rob van den Berg]

Hi all,

When I render a piano staff the curly brackets are too big ...
How do I fix this ?

example pdf :
http://www.robvandenbergmuziekles.nl/index.php?option=com_docman&task=doc_download&gid=37&Itemid=26&mode=view

source :
\paper {
%%  #(define dump-extents #t)

%%  indent = 0\mm
%%  linewidth = 160\mm - 2.0 * 0.4\in
%%  raggedright = ##t
}

\layout {

}

% ly snippet:
\version "2.6.4"
upper = \relative c' {
   \clef treble
   \key f \major
   \time 3/4
\partial 4 c8-1 c
f4-2 f-1 f8 g
\time 2/4
a4 f
\time 3/4
<e-1 g-2>8 [g] g [g]
<< { a8-3 g} \\
{ e4-1 }
>> \break
f2-1 c8 c %% raas, heerl-lijk
f4 f f8 g
\time 2/4
a4 f
\time 3/4
<e g>8 [g] <e g> [g]
<< { a8 g} \\
{ e4 }
>>
\break
f2 f8-1 f  %% vol, ver-
<< {bes4 bes a8 g} \\
{ f2~f8 e}
>>
<f a>2 a8 a
<< {g4 c a8 g} \\
{e2.}
>>
\time 2/4
f2
\break
\time 3/4
f8 [f] f [f] f [g]
<f a>2 a8 a
g4-2 f-1 e8-2 e
f2-1 \bar "|."

}

lower = \relative c' {
   \clef bass
   \key f \major
   \time 3/4
r4
r4
<a-3 c-1>
r8
bes8
\time 2/4
c4 a
\time 3/4
c2
<c bes>4
<a c>2
r4
r <a c> a8 bes
c4 a
c c c8 bes
<a c>2 r4
d2 c4
r2.
<< {c2~c4} \\
{s2 bes4}>>
<a c>2
r4 des2-2
c2-1 r4
<bes c>2.
<a c>2
}

text = \lyricmode {
  Zie de maan schijnt door de bo -- men mak -- kers, staakt uw wild ge -- raas.
  'tHeer -- lijk a -- vond -- "je is" ge -- ko -- men, "'t a" -- vond
-- je van Sint -- ter -- klaas
  }

\score {
  \context GrandStaff <<
    \context Staff = upper {
        \context Voice = singer \upper }
   %% \lyricsto "singer" \new Lyrics \text
    \context Staff = lower <<
      \clef bass
      \lower
    >>
  >>
  \layout {
   %% \context { \GrandStaff \accepts "Lyrics" }
   %%  \context { \Lyrics \consists "Bar_engraver" }
  }
  \midi { \tempo 4=100 }
}

regards,

Rob