I have a 2007 prius with 25,000 miles. I know this may sound funny but it does happen. My car is black and on very hot days if the car has been sitting in the sun. When I get in and shift into drive or reverse the car will shift to neutral. I noticed this when I was in Florida for the month of March. It had not happen until last Friday the temp got up to 85 here in Lacomia, NH. The car had been sitting in my drive way in the sun and when I got in and tried to drive off the car shifted in to neutral. I can hold the shift in drive and drive it and after a while it will act normal again. I think it has to do with the heat build up in the car. Next time I get another warm day I am going to trey leaving the windows down and see if that makes a driffrence.