If things don't go according to plan, and your shifter won't fold properly, take a look at the direction in which the hinge is bending.
To fix it, fold the handlebar down as you normally would to close and apply pressure to the plate. It should correct itself. Caution: notice that the larger casters are folded flat against the unit. This can create a pinch point as the piece snaps back into place, so please keep your fingers clear!
Photo Gallery: