Disklavier

I always thought MIDI was MIDI, but I'm encountering some strange
behavior.

Given a Yamaha clavinova, producing a simple jazz Trio, piano on track
1, drumkit on track 10, and a bass line on track 11.  Plays and sounds
great on the Clavinova.

Spit out a MIDI file, and put it on the Disklavier and the bass line
is gone.  Look at the tracks, and it thinks that track 11 is a "Draw
Organ".

Open the MIDI file on a PC, and it also is confused about track 11,
but has yet another idea about what instrument is there.

Any ideas?

Thanks.
-Kevin