I watched this movie dozens of times and never realized this till just today, and am surprised no one else caught on to this. In the part where Marty goes to meet Doc at the mall, he goes down to the Doc's van, He says hello to Einstein the dog. as he does the back door of the van opens and the Doc backs the DeLorean out and down the ramp, raises the door up and gets out. Well now I wonder how could Doc have gotten in the car while it was in the van when the doors to the car raise up, there no way he could have, do to the lack of room in the van.(this can be noticed in the shot of the car backing out.)