Now watch as I being reason to this and everyone ignores it to just fight with each other. They were leaving ksi and he scans a car to get his new alt mode right? Well who's to say it was a "scanner" car to begin with? perhaps it was a prototype who had scanned a concept camero and was returning to HQ hence the body upgrade.
I don't think they had their prototypes out on civilian roads at that point. Josh says as much when Attinger tells him to send Galvatron and Stinger after the Autobots. It's just what Tonyformer says, he just assumes Stinger's robot form to make the point that he can be just as 'up to date' and 'advanced' as anything the humans can make. And it's not like any of the TFs have been stuck with one bot mode throughout the movies - their bare protoforms bore little resemblance to their resulting body-types after the first scan when they arrived on Earth in TF1, so if they can take on a form then, there's nothing set in stone to say they can't alter it at another time.
