Some of the discription is strange in that no matter where the servo is physically positioned, it always moves 30 deg. This is strange in that the servo should move to some default control signal position when attached.
These are 2 different issues, as I noted in post #2. Re the 2nd half, whenever you start sending pulses to a
servo it will normally jump at maximum speed, because it's unlikely to be at the commanded target position
[except as OP noted, for his particular situation].
Re the 1st half, I have some GWS servos that jump literally 30-deg when power is applied, and NO pulses are
being sent. If I re-apply power several times, I can get the servo to jump a full 180 deg around the clock,
until it gets over to its mechanical stops.