It's gotta be an "auto" thing. I poked around in the service manual and couldn't find anything specifically dealing with that feature, but I did learn that starting this car is a lot more complex than it appears! The car automagically disengages the starter motor when it senses the engine is running, which would explain the cool behavior with the key.

What I did find amusing is the description they give of the starting system:

An electrically operated engine starting system is standard factory-installed equipment on this model. The starting system is designed to provide the vehicle operator with a convenient, efficient and reliable means of cranking and starting the internal combustion engine used to power the vehicle and all of its accessory systems from within the safe and secure confines of the passenger compartment. See the owner’s manual in the vehicle glove box for more information and instructions on the recommended use and operation of the factory-installed starting system.


Like there's any other way to do it!