Looks like a lot of you are having the same fader problem as myself(fader moving down 15-25% on it's own). If you watch the midi signal button when this is happening it blinks meaning a signal is still being sent to your laptop, in other words a Hardware problem, there seems to be a short in the circuit when the fader reaches the top of it's throw.
A fix for this until you have time to send the S4 back, (at the moment i haven't) which stops the problem 100% is to tape a small piece of a rubber band to the top of the fader and let it hang a few millimetres INTO the fader slot, this acts as a rubber buffer and stops the 'short' which is causing the fader to move. If you watch the fader position on screen it still reaches the top meaning no loss of volume. It even seems to improve the feel of the fader because you get a slight bounce as the fader hits full throw. give it a go IT WORKS.