Actually, the spec on the web site is incorrect for the Filter Envelope Generator. The filter EG is a simple A/D, with no sustain - it’s identical to the filter EG in the Taurus 1.
The VCA envelope is an ASD (again identical to the T1). For this envelope, the Decay parameter actually sets the release (fall) time when a note is released. The DECAY footswitch controls whether Decay is ON or OFF (this works like the Release switch on a Voyager). If the footswitch is OFF, there’s no Decay. If ON, the Decay releases according to the Decay EG setting.