midi timings out of sync

[sr]

Is it a known issue that the timings of the midi files created by lilypond
aren't sync'd properly?

Or am I doing something wrong?

I have an ensemble piece (5 instruments).

I've written the piece by creating a separate file for each instrument and
then a "score" file that uses the \include command to combine all of those
individual files into a score.

I have a \tempo marking in each of the individual files, and a
tempoWholesPerMinute in the \midi block of the score file. These are all
marked to quarter = 60.

There are numerous points in the score where the instruments are exactly
synchronized. This is reflected very clearly in the pdf file that is
created, but the entrances in the midi file are way out of sync, as much
as a triplet 8th off. I have confirmed this by looking at the events list
of the midi file in Digital Performer.

Any clues?

Thanks,
Sean Reed
Dublin