Notes in voiceone corrupt voicethree after voice splitting?

[steve]

  Howdy!

             I have reduced a multivoice structure that is part of a
composition to a simple five bar example of voice splitting.
I need 4 voices, and then I need one voice to split.

            Each bar shows a different behaviour depending on the first voice

       bar 1 -   seems ok
       bar 2 -  seems ok and NoteColumn.force-hshift   works in voicethree
       bar 3 -  a quarter note on beat 3 in voiceone causes a collision in
voicethree and NoteColumn.force-hshift doesn't work

       bar 4 - a simple white harmonic in voiceone creates the same
condition as bar 3
       bar 5 - use of     Staff.NoteHead.style = #'harmonic-black  in
voiceone  causes
                  notes in voicethree to change to black harmonics

http://www.gooeytar.com/projects/test/test.pdf

        Obviously, voiceone is messing with the "new voice" in voice three.

        What is the correct way to do this in LilyPond??

     thanx - steve




\version "2.18.2"

H = \once \override Staff.NoteHead.style = #'harmonic-black

voiceone = \relative c'' {
    \clef "G_8"
    \time 4/4
    \key g \major
    b4 b2 r4 |
    b4 b4 r r |
    b4 b b b |
    b4 b b\harmonic b |
    b4 b \H b b |
}

voicetwo = \relative c {
    \set harmonicDots = ##t
    e'8\rest d2..\harmonic |
    e8\rest d2..\harmonic |
    e8\rest d2..\harmonic |
    e8\rest d2..\harmonic |
    e8\rest d2..\harmonic |
}

voicethree = \relative c' {
    <<
        \new Voice  % needed or voiceone and three are fused
        {
         s4 g4^~ g2 | s4 g4^~ g2 |
         s4 g4^~ g2 | s4 g4^~ g2 | s4 g4^~ g2 |
        }
   %    \\
        \new Voice
        {
         \stemDown
         g4\rest g4 fis2 |
         g4\rest g4
         \once \override NoteColumn.force-hshift = #2.0      % to prove it works
here
         fis2 |
         g4\rest g4
         \once \override NoteColumn.force-hshift = #2.0       %  doesn't work 
here
         fis2 |
         g4\rest g4 fis2 |
         g4\rest g4 fis2 |
        }
    >>
}

voicefour = \relative c {
    c1 | c1 | c1 | c1 | c1
}

 guitar = << \voiceone \\ \voicetwo \\ \voicethree \\ \voicefour >>

#(set-global-staff-size 19)

\score { \new Staff \guitar }