Dilemma with spacer rest and cross-staff polyphony.

[Hwaen Ch'uqi]

Greetings:
     As you will see from the attached pdf file, the center two
measures differ from the intention of the code shown below. The upper
voice is treated as if it is in bass clef. I would be grateful for any
advice. Has it possibly something to do with the interaction of the
preceding spacer rests with the corresponding cross-staff activity?
Many thanks.
Hwaen Ch'uqi

\version "2.12.3"

  \paper{
    #(set-paper-size "letter")
  }

\score{
  \new PianoStaff<<
    \new Staff = up {
      \key a \major \time 4/4 \clef treble \relative{
        s1*2
        <<
          {
            d'4. e!8 fis4 gis8 a!
            b4 e, s2
          }
          \\
          {
            cis,8*2/3 \change Staff = down \stemUp fis, ais b cis d \change
Staff = up \stemDown e \change Staff = down \stemUp eis fis \change
Staff = up \stemDown d' e cis
            d e cis cis d b b dis, e e \change Staff = down \stemUp dis, e
          }
        >>
        s1*2
      }
    }
    \new Staff = down {
      \key a \major \time 4/4 \clef bass \relative{
        <<
          {
            dis,8*2/3 cis' \change Staff = up \stemDown fis eis' cis fis
\change Staff = down \stemUp a,, bis \change Staff = up \stemDown fis'
a' bis, gis'
            \change Staff = down \stemUp gis,, bis \change Staff = up
\stemDown a' fis' gis, eis' \change Staff = down \stemUp gis,, cis
\change Staff = up \stemDown fis dis' eis, cis'
            \change Staff = down \stemUp s1
            b,4 cis d2
            d,!8*2/3 b' \change Staff = up \stemDown a' a' b, g' \change
Staff = down \stemUp d,, b' \change Staff = up \stemDown g' g' a,
fis'!
            \change Staff = down \stemUp b,,, g' \change Staff = up \stemDown
fis' fis' g, e' \change Staff = down \stemUp a,,, g' \change Staff =
up \stemDown a b' e, a
          }
          \\
          {
            a,,2 gis
            cis, cis'4 bis
            b2 ais
            <a! f'> <gis e'>
            fis! e
            d cis
          }
        >>
      }
    }
  >>
  \layout{
    \context {
      \Score
      \remove "Bar_number_engraver"
    }
  }
}

Test.pdf
Description: Adobe PDF document