Problem with Hara_kiri_engraver

[Dominic Sacré]

Hi,

I have a score with a similar structure as the example attached below.

This seems to work fine, the output is correct, but I get lots of warnings 
"Symbol is not a parent context: Staff. Ignored", apparently one for each 
note in the first staff.
What does this warning mean, and how can I get rid of it?

I only get these warnings with lilypond-1.5.67, version 1.4.12 of lilypond 
did not complain...

Thanks in advance,
    Dominic

--------------------------------------------------

\paper
{
  \translator
  {
    \StaffContext
    \name HaraKiriStaff
    \remove "Axis_group_engraver"
    \consistsend "Hara_kiri_engraver"
  }
  \translator
  {
    \ScoreContext
    \accepts HaraKiriStaff
  }
}

\score
{
  \context GrandStaff
  <
    \context HaraKiriStaff = first
    {
      \notes { R1 | c'4 d'4 e'4 f'4 }
    }
    \context Staff = second
    {
      \notes { c'4 d'4 e'4 f'4 \break c'4 d'4 e'4 f'4 }
    }
  >
}