When I use my S2a it feels like the camera's going to ruin each shot by moving, but the reality is that all of the hard movement takes place after the shutter has closed. If you are actually seeing the lens move and you're sure it's on the mirror-up part of the cycle, then there's something seriously wrong.
I've had no problems hand-holding and getting sharp negatives with the S2a down to 1/30th of a second consistently, and at 1/15th about 80% of the time. The camera always feels as if each shot is ruined, but the negatives are tack-sharp. A year or two ago I finally decided to do some real investigating on the system. I found that the camera is very steady up until the moment the shutter closes, then all hell breaks loose. The jarring movements all occur after the image is safely on the negative.
By the way, what do you mean by an "out of sequence serial number"?