acciaccatura on lieder set

[Robert Garrigos]

Could someone tell me what I am doing wrong with this lieder set? When using 
acciaccatura in the beginning, I’m getting wrong ouput:

this code:

global = {
  \key g \major
  \time 3/4
}

\score {
  <<
    \new Voice \relative c' {
      \global
      g'2.
    }
    \new Lyrics \lyricmode{
      a
    }
    \new PianoStaff 
    <<
      \new Staff  \relative c' {
        \global
        % | \override Flag.stroke-style = #"grace" cs8(  <d) b g>2.
        % | <d b g>2.
        | \acciaccatura cs8  <d b g>2.
      }
      \new Staff  \relative c' {
        \global
        % | \override Flag.stroke-style = #"grace" cs8(  <d) b g>2.
        % | <d b g>2.
        | \acciaccatura cs8  <d b g>2.
      }
    >>
  >>
}

gives me:


whenever I take the acciaccatura out or substitute it with the  \override 
Flag.stroke-style = #”grace”, the output is ok. Also, deleting the voice and 
lyric lines, the output is ok. What’s wrong with my first code?

thanks.

Robert