\chordmode chords jumping about on PDF

[James]

Hello

I am using Mac OSX Snow Leopard (10.6.x) with LilyPond 2.13.35

Here is the smallest example I could get down to

--

\version "2.13.35"

RH = \relative c'' {
    \repeat unfold 30 { a8 a a a }
}

LH = {
   \clef bass
   \repeat unfold 30 { a8 a a a }
}

\score {
   \new PianoStaff
   <<
    \chords { f1*5 bes :m }
    \new Staff  \RH
    \new Staff  \LH
   >>
}

---

The symptom is after each compile the chord symbols move 'randomly' up 
and down on the next PDF output. No changes are made to the .ly file, 
the file is just compiled again and the chord symbols move.

If I use

    \chords { f1 bes :m } instead (as a test) then the jumping about 
isn't so weird - that is it does still jump up and down but it seems to 
be consistent - but it occurs every time I recompile.

All other notes in the score are fine.

I have attached a small screen-shot to show you what I mean, from left 
to right is the output of the PDF after each compile.

There is no pattern I can see, occasionally I get a message about
--

Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
programming error: insane spring min_distance requested, ignoring it
continuing, cross fingers
Layout output to `test.ps'...
Converting to `./test.pdf'...

--

But there is no correlation to this message and the output.

Also I have tried this same file on Windows 7 and cannot (yet) get this 
to occur.

regards

James

screengrabs.jpg
Description: JPEG image