\version "2.11.38"

% taken from http://lilypond.org/doc/v2.11/Documentation/user/lilypond/New-dynamic-marks#New-dynamic-marks
rndf = \markup{ \center-align {\line { \italic ( \dynamic f \italic ) }} }
rndp = \markup{ \center-align {\line { \italic ( \dynamic p \italic ) }} }

% colla parte music:
mus = \relative c' { e4-\rndf f g a-\rndp g f e d}

\score{
<<
  % the violin part:
  \new Staff <<
    \new Voice = vvI  << \dynamicDown \mus >>
  >>
  % the vocal staff:
  % Vocal staves should have the dynamics above (so they don't collide with the lyrics!!!)
  \new Staff <<
    \new Voice = vvII << \dynamicUp \mus >> % <== This does NOT work, i.e. the (p) is still below the staff
  >>
 >>
}