My Model S is brand new. The first time I tried to use Auto Lane Change, she started to move into an occupied lane. My hands were on the wheel, so no disaster occurred, but I was shocked. I presumed that the AP-2 hardware and software would assure that there was no car adjacent to mine or overtaking it in the adjacent lane before starting to steer into it. Was this a malfunction, or is it completely up to the driver to make sure that it's safe to change lanes?