Why do these chords not line up vertically?

[ivan . k . kuznetsov]

In this example, why does the lowest voice not line
up vertically with the first five chords?

What do I need to do to make this voice line up?

Thank you for your help.


\version "2.16.0"
\include "english.ly"

\score {

  \new Staff
  {
    \time 4/4
    \clef "treble"
    <<
    \voiceOne
    {
       \stemUp
       bf'1   ef''1  ef''1  gs''1  af''1  cs'''1
    }
    \voiceTwo
    {
       \stemUp
       g'1    g'1   c''1    c''1   f''1   f''1   
          
    }
    \voiceThree
    {
       b1     e'1   e'1     a'1    a'1    d''1   
    }
    >>
  }
}