At the end of CD1, after you kill Jenova *LIFE, and your party is staring at (SPOILER)Aeris' corpse , if Vincent is in the third slot of your party, his graphics will completely mess up. His cloak and his right leg will be upside down, and he will walk weirdly. I believe this is a consequence of the collision applied to the narrow space in which he is standing, probably not prepared to have him around.
Try it!