Lately I have noticed a number of drivers who have entered the intersection on the green traffic light intending to make a left turn and then backed up instead of turning once the light has changed to red. This sometimes happens with through traffic in an intersection as well. In either case, backing out of the intersection is unsafe and may be illegal.
If you are through traffic stuck in an intersection when the traffic light turns red it probably means that you have not been looking far enough ahead to anticipate what might happen. I was taught that the farther down the road you see while driving, the less likely you are to have a collision. Or, in a case like this, the less likely you are to be caught blocking an intersection when the lights change.