lilybond-book staffsize problem

[Johannes Heinecke]

Dear all,

I have stumbled over en problem with lilypond-book 2.8.1: 
Using 
\begin[staffsize=11,line-width=128\mm]{lilypond}
\include "../mySong.ly"
  \score {
      \new Staff = devenu <<
        \context Voice = "sopranos" \sopranRefrain 
        \context Lyrics = sop \lyricsto sopranos \textRefrain  >>
  }
\end{lilypond}

The staff has the desired size (11pt), but the notes, clefs etc. are still at
20pt. When I use lilypond on its own (i.e. not lilypond-book) all is fine. Did I
miss anything to rescale note-symbols as well?

Best regards
Johannes