There is no such thing as ambient lighting in the realworld. Since the games are using ambient lighting and not direct light sources, they have to compute a shadow somehow. That's where ambient occlusion comes in to give the object depth. There is no ambient occlusion being used on the individual characters. That is, there is no rays being shot out into the scene on the coat or shirt or shoes, for example, to test occlusion.
Sorry but you are just talking without understanding what is going on. Literally global ILLUMINATION in name has information for you about what it is doing. Ambient occlusion has nothing to do with how characters are lit but with darkening of space between two close objects like when you lean on wall that part of wall occluded and thus its ambient color darkens.
Characters being weirdly lit literally has nothing to do with ambient occlusion but with their global illumination not updating properly in that scene.