Incorrect voice combining when using PianoStaff and Staff changes

[Thomas CHARDIN]

> I'm not top posting.

Hi,

I would like to combine every possible note heads on the following example but
the behaviour of Lilypond seems erroneous :

\version "2.14.1"

\score {
  \new PianoStaff <<
    \new Staff = "up" {
      \clef G
      \key ees \major
      \time 6/8
      \autoBeamOff
      <<
        {
          f'4. e'4. |
          ees'4.~ ees'4 d'8 |
        } \\ {
          \change Staff = "up" f'16[ c' \change Staff = "down" a f c f,] \change
Staff = "up" e'16[ c' \change Staff = "down" a f c f,] |
          \change Staff = "up" ees'16[ c' \change Staff = "down" a f c f,] c16[
f a \change Staff = "up" c' d' \change Staff = "down" fis] |
        }
      >>
    }
    \new Staff = "down" {
      \clef F
      s2.*2
    }
  >>
}

Thanks for any advice,


Thomas