stemUp causes force-hshift to be ignored

[Sean O'Donnell]

Why does \stemUp cause the force-hshift to be ignored? In the example  
below, if I remove \stemUp, force-hshift will work. But not as it is.

Thanks,
sean



\version "2.11.17"

\score {

\relative c'' {
\time 4/4
\key e \minor
\clef treble
\override Fingering  #'padding = #0.3
\set fingeringOrientations = #'(left)
\set stringNumberOrientations= #'(down)

% See middle voice - move a4 to right and flip its stem up
<< { b1 } \\
{ \once \override NoteColumn #'force-hshift = #1 \stemUp a4 g8 fis  
g2 } \\
{ \stemDown e2 e,4 e' } >>

}

}