extra-offset and finger changes

[Mark Alexander]

I'm fairly new to Lilypond, and am using version 1.6.6. on Mandrake
9.0.  I have been studying the Brahms Intermezzo example for clues on
how to adjust the vertical placement of finger changes.  I can
successfully move single fingerings, but ones that involve two fingers
(i.e. a finger change) stubbornly refuse to move when I attempt
to set extra-offset.

Here's my test input:

\score
{
  \notes
  <
    \context Staff = staffA
    {
      \clef treble
      \time 4/4
      g'4-1                     % This fingering appears above the note
      g'4-#'(finger "1-5")      % This fingering appears below the note
      \property Voice.Fingering \set #'extra-offset = #'(0 . -1.8)
      g'4-1                     % This fingering gets moved down
      g'4-#'(finger "1-5")      % But this one doesn't move at all
    }
  >
  \paper { }
}