I would think the bending risk would apply more to the metal track holding the window than the window itself... either way, tempered safety glass doesn't follow the same rules as ordinary tin or lead float glass-- you could leave that sheet standing straight up for a thousand years and it won't start to trickle.

Returning to the original question, you have a ground somewhere that isn't 100% effective. So energy is left in the chassis of the car following shutdown, until you liberate it by forming the ground-- with yourself. My old Mitsu used to shock the hell out of whoever got out first. Which tended not to be me.