not break in period lah. Is a safety feature. Dont want owner to do launch control. 
mine only jerks when traffic jam and I am picking up speed. No jerking occur when I release pedal to slow down.

Although both FLX and Sylphy is using CVT, but both CVT system are different. FLX CVT system has a clutch in it and Sylphy (Xtronic) is using torque converter. If you have driven a MT car before, you should know what will happen when you "play" with the clutch (ie, engage and disengage, engage then disengage). Your car will jerk too. Instead of thinking it as a conventional AT, I recommend you to treat it like a MT transmission with a "robotized" clutch. During pick up, the clutch will slowly disengage till a specific speed. During slow down, the clutch will gradually engage back and hence the engine braking occurs. The sudden throttle input and output, coupled with the laggy drive by wire system causes the clutch to engage then disengage then engage again and this is the reason why the jerk occurs during traffic jam.

Nothing much can be done to minimize this issue because this is the weakness of clutch based CVT but the benefit it offers is lesser power loss than a torque converter CVT. Boleh vroom vroom.