The original Prophet VS manual say this about Unison mode: "If Unison/Detune is on, all eight voices are assigned to the last played, for a "fat" sound."
I read this as the envelopes should retrigger also when botes are played legato. However that's not happening in Arturias Prophet VS. So that seem to be a bug.
In Arturias Prophet VS the play mode MONO does retrigger the envelopes, while the LEGATO does'nt. That indicate that Arturias Prophet VS UNISON work like the LEGATO and not like the MONO playmode. That to me also indicate it's a bug that UNISON should trigger the envelopes even when playing Legato.
Am i missing something? It can be very annoying not to have retrigger when using UNISON. I would'nt mind the option for both though,