This is also caused by an incorrect comm port setting. Refer to the "What Comm Port Do I Use" section to determine the correct comm port number. Turns out that some laptops have a comm port that echos everything back into the Rx buffer. I have no idea why or how. With this loopback port, you are not sending any traffic out the EAS Serial Cable. In fact, with this loopback comm port number, you could run the laptop inside not connected to anything and you would get the exact same behavior. Spend some time in the Windows Device manager and find the correct comm port to use.
Video: What Comm Port Do I Use