\override NoteColumn #'force-hshift ignores \stemUp

[leoninus]

Hi,
  it seems that  \override NoteColumn #'force-hshift ignores a \stemUp
command when this follow it
  see below (Mendelssohn op. 65 no. 1 first mov.)

ManualTwoVoiceTwoMusic = \relative c {
  \partial 2 
  <c e>2~ | <c ees!>  des | aes1 | 
  <<{\stemDown r4 r8 c~}\\
  {\once \override NoteColumn #'force-hshift = #1 \stemUp c4. c8~}>>   c2|
f2 
}

In the same example the last note c8~ is not tied with the following c2 out
of the polyphonic context.
I am using wrongly it?

 Thanks in advance
Leoninus

  I

===
  \begin[quote,staffsize=14]{lilypond}
TimeKey = { \time 4/4 \key f \minor }
ManualOneVoiceOneMusic = \relative c' {
  \partial 2
   c2 | << { ees f | ees aes |  aes  g} \\ {ees2.  des4~ |des c2 des4 | 
ees2 bes}>>  | aes'2
}
ManualOneVoiceTwoMusic = \relative c' {
}
ManualTwoVoiceOneMusic = \relative c' {
  \partial 2 
  g2~ | g4 aes2. | r4 << {aes2.~}\\{aes4 ees f}>> | aes2 d,8 f e g | f8 aes
c8 
  \change Staff = "ManualOne" \stemDown f8_\laissezVibrer \stemNeutral
  \change Staff = "ManualTwo"
}

ManualTwoVoiceTwoMusic = \relative c {
  \partial 2 
  <c e>2~ | <c ees!>  des | aes1 | 
  <<{\stemDown r4 r8 c~}\\
  {\once \override NoteColumn #'force-hshift = #1 \stemUp c4. c8~}>>   c2|
f2 
}

PedalOrganMusic = \relative c {
  r2 | r1 | r1 | r1 | r2
  }

\score {
  <<  % PianoStaff and Pedal Staff must be simultaneous
    \new PianoStaff <<
      \new Staff = "ManualOne" <<
        \TimeKey  % set time signature and key
        \clef "treble"
        \new Voice { \voiceOne \ManualOneVoiceOneMusic }
        \new Voice { \voiceTwo \ManualOneVoiceTwoMusic }
      >>  % end ManualOne Staff context
      \new Staff = "ManualTwo" <<
        \TimeKey
        \clef "bass"
        \new Voice { \voiceOne \ManualTwoVoiceOneMusic }   
        \new Voice { \voiceTwo \ManualTwoVoiceTwoMusic }        
      >>  % end ManualTwo Staff context
    >>  % end PianoStaff context
    \new Staff = "PedalOrgan" <<
      \TimeKey
      \clef "bass"
      \new Voice { \PedalOrganMusic }
    >>  % end PedalOrgan Staff context
  >>
}  % end Score context
\end{lilypond}
===
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