autochange with multiple voices

[Nik Repka]

> I'm not top posting.

I am following the syntax of this snippet: 
http://www.lilypond.org/doc/v2.15/Documentation/snippets-big-page#keyboards-using-autochange-with-more-than-one-voice.
 But in my file, autochange is only applied to the top voice, and it drags
the other voice with it to the "up" staff.

What am I doing wrong?

\version "2.18.2"

scaleRH = \relative c' {c d e f g a b c c b a g f e d c
g a b c d e fis g g fis e d c b a g}

scaleLH = \relative c {c d e f g a b c c b a g f e d c 
g a b c d e fis g g fis e d c b a g}


\score {
   \new PianoStaff 
    
      << \new Staff = "up"
         <<
           \new Voice {
           \voiceOne
           \autochange
    
           \scaleRH 
           
           }

           \new Voice {
           \voiceTwo
           \autochange
           \scaleLH 
           }
         >>

      \new Staff = "down" { 
          \clef bass
      }
      >>
}