I had a similar problem while using Cubase a few years ago. Pushing play to listen to a midi track on my synth resulted in a program change to 00. It turned out to be a (very well hidden) program change command in the midi track. I've since found that I can just turn off program change in Cubase. Perhaps Ableton will do the same?
Keith
Thank you for your answers.
Indeed the problem comes from Ableton, but not directly from Ableton.
It is by importing a midi file from Avid Sibelius (score editor) which, when importing, places the program of the imported midi track on 1 by default.
This has the effect once in Ableton of forcing the return to the 1st program when the midi data is sent to the Prophet 6 (program 00).
Simply disable the function directly in the options offered by Ableton (clip> launch>pgm--), of the imported midi sequence to disable the command.