unexpected octave oddity

[Jay Hamilton]

Can anyone explain why the notes in the bass line don't follow the rules that I 
understand the b following the a should be in the same octave shouldn't it?
\version "2.12.2"
\header {
  title = "Silence"
  subtitle = "an Opera; for 5 voices and chamber Orchestra"
  subsubtitle = "unfortunately the time signature is irrelevant"
  composer = "Jay Hamilton"
copyright = \markup { \tiny \override #'(baseline-skip . 0.5)
\center-column
        {  "CC lic 2.5 some rights reserved Jay Hamilton 2009"
    "see http://creativecommons.org/licenses/by-nd/2.5/";
               } }
               }

global = {
  \key c \major
  \time 4/4
}
sopranonotes = \relative c' {
cis8 fis a gis b a gis gis fis2. r4 r1 r 
r4 a8 cis b4 dis8 cis ~ cis r8 

}

sopranowords = \lyricmode { 
There was a child who wrote a sto- ry
what made him write that?
  
}

altonotes = \relative c'' 
{
r2 b,8 dis cis4 ~ cis16 e fis8 gis4 r4. e8 [f! cis]
e2 r4 r2. r8 fis cis4 r8 r2

}
altowords = \lyricmode 
{ At the time peo- ple thought it  pre- co- cious
won- der

}
tenornotes = {
  \clef "G_8"
r1 r4.. 
\times 2/3 {e8 f! b} a4 f16 ~  [f b a8] ~ a4 r2
r2 r8 cis'8 b4 r2 r8 a b gis a b cis4 (r8)

   }
tenorwords = \lyricmode {
 con- sid- ered it  pre- co- cious
 won- der What made him write like that?

 }
tenorIInotes = {
  \clef "G_8" 
 r1 r8 cis8 fis4 a8 gis4 e8 f!4 gis8 fis cis4 r4 
 r2 r8 a fis4 r1   
  
  }
tenorIIwords = \lyricmode { 
There was a child who wrote a stor- y
won- der

}
bassnotes = {
  \clef bass 
  r1 r r2 r8 a, b4 
  a8 cis b a fis' cis4 r1 a8 dis4 e8 gis,4
  }
basswords = \lyricmode {
 That made
 the oth- er kids won- der What makes a chi- ld?

 }

\score{
  \context ChoirStaff
  <<
    \context Staff = soprano <<
      \context Voice = sopI { << \global \sopranonotes >> }
    \set Staff.instrumentName = #"One "
      \lyricsto "sopI" \new Lyrics \sopranowords
    >>
    \context Staff = alto <<
      \context Voice = altII { << \global \altonotes >> }
      \set Staff.instrumentName = #"Two "
      \lyricsto "altII" \new Lyrics \altowords
    >>
    \context Staff = tenor <<
      \context Voice = tenIII { << \global \tenornotes >> }
      \set Staff.instrumentName = #"Three "
      \lyricsto "tenIII" \new Lyrics \tenorwords
    >>
    \context Staff = tenorII <<
      \context Voice = tenIV { << \global \tenorIInotes >> }
      \set Staff.instrumentName = #"Four "
      \lyricsto "tenIV" \new Lyrics \tenorIIwords
    >>
    \context Staff = bass <<
      \context Voice = basV { << \global \bassnotes >> }
      \set Staff.instrumentName = #"Five "
      \lyricsto "basV" \new Lyrics \basswords
    >>
  >>

}
 Thanks
Jay


Yours-
Jay

Jay Hamilton
www.soundand.com
206-328-7694