programming error: Going back in MIDI time

[Peter O'Doherty]

Hi,
I know this has been asked before but I haven't been able to resolve it 
satisfactorily. Can anyone suggest a solution to this error?
It occurs in the example below, i.e. when the grace note has more than 4 
members.
Many thanks,
Peter

##################
\version "2.12.3"
\include "english.ly"

upper = {
  \clef treble
  \time 4/4
  %a'8[ a' a' a'] \acciaccatura { c'8[ d' e' f' g'] } a'8[ a'8 a'8 a'8 
] %doesn't work
  a'8[ a' a' a'] \appoggiatura { c'8[ d' e' f'] } a'8[ a'8 a'8 a'8 ] %works
}

lower = {
  \clef bass
  f4 f f f
}

\score {
  \new PianoStaff
<<
    \set PianoStaff.instrumentName = #"Piano"
    \new Staff = "upper" { \upper
     }
    \new Staff = "lower" {\lower
    }
>>
   \layout {
     \context {
          }
   }
   \midi { }
}
##################