Actually, the real cause is: The sensor on your gas cap is extremely sensitive. You just need to unscrew it. Then screw it back on until you here the small click that is fully sealed. Soon after, drive around the block (7 - 15 minutes), then park. Turn the car off, and turn it back on. Voila, sensor is back to its proper, working function.
The reason it does that is due to the car being so light, so a lot of the shifts in transmission(s) is/are felt among the gas cap sensor (this sensor is very, very sensitive).
Anyway, I suggest that you drop the rental, get your FR-S back, and be excited that it is just a sensor "sensitivity" issue!
