troubles with vertical staff distance

[Herbert Liechti]

Hello all

I have some problems to get a vertical distance between
to staffs:


Everything went ok from the second line in sheet:


I'm attaching a stripped down version of the score. I tried
the code in the snippet archive http://lsr.dsi.unimi.it/LSR/Snippet?id=225
But when using this code a third staff is inserted with a treble
key.

I'm using version 2.11.34

Thanks you for help
best regard Herbert

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\version "2.11.34"
\paper{ 
    ragged-bottom = ##t
    printallheaders=##t
}

stimmedrei  =  {
        \key bes \major
        \time 3/4

    \relative c' { 
       r2 d8. es16 | 
       f4 d bes8. bes16 |
       a4 g es'8. c16 |
       d4 bes c |
       bes r4 f8. f16 |
       \repeat volta 2 {
          bes2 bes4 |
          c2 a8. a16 |
          bes4 a a |
          bes2   f8. f16 |
          f4 bes bes  |
          bes2\fermata c8. c16 |
          bes2 a4 |
       }
       \alternative {
          {
             bes2 f8. f16 |
          }
          {
             bes4 c4 d8. d16 |
          }
       }
       d4 c d |
       bes2 a4 |
       bes2 bes4 |
       bes d es |
       d2.\fermata |

      
   }
}
bassstimme  =  {
        \key bes \major
        \time 3/4

    \relative c { 
       r2. |
       d4 f g |
       f es g |
       f d es |
       d f2 |
       \repeat volta 2 {
          f2 d4 |
          a'4 f2 |
          f2 f4 |
          f4 f2 |
          bes,8 c d4 d8 f |
          g2\fermata g8. a16 |
          bes2 f4 |
       }
       \alternative {
          {
             f4 f2 |
          }
          {
             f4 g e8. e16 |
          }
       }
       f4 es d |
       f2 f4 |
       f2. |
       g2 g4 |
       bes2.\fermata |

      
   }
}
leaddrei =  {
   \set Staff.instrumentName = "Trombone I"
    \clef bass
    \stimmedrei
}
basseins =  {
   \set Staff.instrumentName = "Trombone II"
    \clef bass
    \bassstimme
}
     
   \header {
       breakbefore = ##t
       title = "Happy Birthday (Cumpleanos Feliz)"
       composer =""
       instrument = "Partitur"
       arranger = \markup { \tiny {"Arr. David Romero"}}
   }
\book {
   \pageBreak
   \pageBreak
   \header { instrument = "" }
   \score {

      %% Tb I + II
      <<

             \new Staff \leaddrei 
             \new Staff \basseins 
      >>
      \header { instrument = "Trombone I + II" }
   }
}