«The envelopes have a different behaviour – the attack does not reset 0 at the beginning of each note, but rather starts from the current level of the envelope.»
is this why the duophony mode act strangly now ?
press and sustain the low note
press the high note, release it => it is like the high note is restarted (instead of hearing only the low note)
No, this is unrelated. The duophonic mode has always acted strange 
Ok, I have found something that has changed…
Postmortem:
When you played and held a note, then a second one, then release the second one, the first note is retriggered (“stack retriggering”). It used to be retriggered with velocity = 0 (because the note stack didn’t store the velocities and there was no way of traveling back in time to know at which velocity it was originally played). Someone complained about this, so I made the change to the note stack to store the velocities, and since v0.97, the note is retriggered at its original velocity.
The problem is that the duophonic mode used the velocity = 0 information to distinguish between true triggers and “stack retriggers”. After this change, the duophonic mode had no way of distinguishing a true trigger from a “stack retrigger”, and this caused spurious retriggers.
Duophonic mode is fragile, arghh
Anyway, updated .hex / .syx / .mid file here.
so fragile and so beautifull
merci, it works !
on dirait que j’ai deux comptes différents, mais je suis la même personne qui a posé la question 8)