I've had my Tesla S just a few weeks. I charge it from a 50 amp outlet in my garage. Sometimes when I push the button on the car end of the cable to unlock it, instead of turning white and unlocking the port goes through a rapid sequence of colors - blue, red - and then returns to green. If I push the button again it finally turns white and lets me remove the cable. Is this normal? If not, what am I doing wrong?