If you're using a sequencer, I've found that if you have A set too high, the notes start to cut out, because the A time is longer than the sequencer's gate.
But that's not what you're talking about, is it?
As a side note, it took me some experimentation to realize that the Sustain fader only works going "down", not "up". That is, if I want a manual volume swell, I need to do it with the volume knob, but a manual fadeout works from the ADSR.
I hope you get a good resolution to your problem.