Serial Communication with MATLAB

Hi, I am using a MATLAB controller to compute actuator motion and send it to the Dymanixel controller via Serial communication. It usually works well but I noticed that sometimes when I upload the Arduino code, the actuator would move even though the MATLAB is not running. (I cleared all data as well). Please can anyone give some suggestions on this?

Hardware: Dynamiel OpenCM 9.04 + exp485 board + MX-64AR motors
Software: MATLAB code to compute actuator motion; Arduino code with Dynamixel2Arduino library; communication successfully established via Serial communication