Actually, it was the windshield thing. It just doesn't want to actually meet with the hood. I really wish they put some text in the instructions. I know I've said it before, but it could clear up some of the more ambiguous panels.

The riding thing was my daughter's idea. "Hey, he can ride his friend!" What's really cool, though, is that she identified them as Optimus Prime and Bumblebee without me mentioning it. And she can't identify the movie pretenders who use the same name, so she knows the "real" deal.