It appears that envelope 3 doesn't reset its value on a key trigger unless the is at least a small amount of delay added to the envelope.
(The envelope will just continue from wherever it is from the previous A/D/S/R cycle.)
I'm not complaining. It's a nice feature. And it may be standard DADSR envelope behavior for all I know. (first one of these I've seen)
But it would be nice to see a blurb about in the manual.