Switching from one staff to two staffs

[Adrian Mariano]

I want to typeset something which starts out with just one staff and then
harmony comes in and there are two staffs.  I can't figure out how to do
this.  I get an extra blank staff during the second section (using
Lily 1.1.15):


\include "english.ly"


\score{
  \notes {
    \type Staff=first \relative c'{ \key bflat; \time 3/4;
    % plucked string instrument
    bf2 bf4 | d2 ef4 | f2 ef4 | d8 f()f2 | bf,2 bf4 | d2 ef4 | f2 ef4 |
    d4. [ f8 d bf ] | [c bf] af4 [c8 bf] | [c8 bf] af4 ef' | f2 ef4 |
    c8 af8()af2 | bf2()bf8 bf8 | d8 f()f2 | c2. | bf2. \bar ".|";
    \break
    % flute
    d8 f8()f2 | bf2 f4 | g4 ef2 | f8 bf,8()bf2 | d8 f8()f2 | bf2 f4 |
    g8 ef2 [f16 g] | f2()f8 bf | f2. bf,2 [d8 ef] | ef2 f4 | 
    c8 af8()af2 | bf2. | d8 f8()f2 | c2. | bf2. \bar ".|"; |
    \break
     }

     \type StaffGroup <
     \type Staff=first \relative c' { \key bf; \time 3/4;
       \property Score."midi_instrument"="church organ"
       f2 f4 | bf2 g4 | af2 g4 | f8 bf8()bf2 | r4 f4 f | bf2()bf8 g8 |
       af2 g4 | f2. | ef2 ef4 | ef2 ef4 | f2 g4 | af2 g4 | r4 g f | 
       f2. | ef2 c4 | bf2. | \break

       d2 f4 | bf2 f4 | g2()g8 ef8 | f8 bf,8()bf2 | r4 d4 f4 |
       bf f2 | g4 ef2 | f2. | f2 f4 | bf,2 d4 | ef2 f4 | 
       c8 af8()af2 | bf2()bf8 bf8 | d4 f2 | c2. | bf2. |
     }
     \type Staff=pipes \relative c' { \key bf; \time 3/4;
       \property Score."midi_instrument"="bagpipe"
       bf2 bf4 | d2 ef4 | f2 ef4 | d8 f8()f2 | bf,2 bf4 | d2 ef4 | f2 ef4 |
       d2. | c2. | c2()c8 ef8 | f2 ef4 | c8 af8()af2 | bf2()bf8 bf8 |
       d8 f8()f2 | c2. | bf2. |

       d8 f8()f2 | bf2 f4 | g2 ef4 | f8 bf,8()bf2 | d8 f8()f2 | bf2 f4 |
       g8 ef2 [f16 g] | f2()f8 bf | f2. bf,2 d4 | ef2 f4 | 
       c8 af8()af2 | bf2. | d8 f8()f2 | c2. | bf2. \bar ".|"; |
     }
  >
  }
  \paper{ indent=0.; }
  \midi{ \tempo 4 = 120;}
}