No midi with lilypond-book

[Clifford Racz]

I am using v. 2.10.33 and I am getting no midi output when using 
LilyPond-book (i.e. \include "lilypond-book-preamble.ly" ).

-------------------------------------------------------------------------------
%Example that works
\version "2.10.33"
\include "lilypond-book-preamble.ly"
\score {
  \context PianoStaff <<
    \new Staff = "treble" << \relative c'' { a b c d e f g a' } >>
  >>
  \midi { }
}
-------------------------------------------------------------------------------
%Example that is broken
\version "2.10.33"
\score {
  \context PianoStaff <<
    \new Staff = "treble" << \relative c'' { a b c d e f g a' } >>
  >>
  \midi { }
}
-------------------------------------------------------------------------------

Is there a fix for this issue?

I saw in the mailing archives that Christian Torff wrote twice regarding 
this issue:

Mon, 17 Jul 2006 05:19:47 -0700
Thu, 22 Jun 2006 11:41:03 -0700