While using the variable cruise control i was following a car which was traveling 40mph. i had my variable cruise control setting at 75mph and the maximum distance setting. therefore i was traveling at 40mph. a motorcycle passed me on my right going 50mph+. as my car recognized the motorcycle in front of me it slowed initially, and then accelerated to follow the motorcycle. the acceleration continued after the motorcycle had passed the car in front of me. it seems that the variable cruise control remained focused on the motorcycle although there was now a car between me and the motorcycle. the acceleration continued and the distance between me and the car in front of me decreased until i interrupted the cruise control and slammed on the brakes. this scenario has occurred several times. this all occurred on a highway in the carpool lane while going straight.