Note-heads not superimposed

[David Sumbler]

In the piece I am setting there is some perhaps slightly unorthodox
notation.  One bar is still giving me a problem.  I attach the output
of this and the following bar.

I am quite pleased with the result apart from one detail: the last
quaver of the first bar should appear as a single notehead on C.  As it
is, 1 of the 2 noteheads is being shifted, despite my \shiftOff
instructions.

The code is this:

%%%%%%%%%%%%%%%%%%
\version "2.19.48"

\language "english"

lv = \laissezVibrer

\new PianoStaff <<
  \new Staff = "RH" {
    \set PianoStaff.connectArpeggios = ##t
    \time 2/4 <<
      { \stemUp
        e''2\arpeggio | s8 }
      \new Voice { \shiftOff \stemDown
                   <b' g'>4\arpeggio ~ \set tieWaitForNote = ##t
                   \stemUp \tuplet 12/8 { <b' g'>32 b'\lv g'\lv e'\lv
                                          \change Staff = LH b\lv g\lv
c g b
                                          \change Staff = RH e'_~ g'
b'_~ } |
                   <e'' b' e'>8-. } >>
    \oneVoice <ds'' b' a' fs'>8-. <e'' b' g' e'>4\fermata \bar "||" |
  }
  \new Staff = "LH" {
    \clef "bass" \time 2/4
    << { \shiftOff <g e c>4\arpeggio ~ \stemDown q8\noBeam c <c g b>-.
}
       \new Voice { \shiftOff \set tieWaitForNote = ##t
                    \hideNotes \stemUp s4.
                    \once \override TupletNumber.stencil = ##f
                    \tuplet 3/2 { c32~ g~ b~ } s16 <b g c> }>>
    \oneVoice <b b,>8-. <b e>4\fermata |
  }
>>
%%%%%%%%%%%%%%%%%%

How do I get the triplet demisemi and the quaver to share the same
notehead?

David

test.pdf
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