Scenery developers don't have any control over the autopilot behaviour. We can only set the ILS according to real life specs, and they surely are at KORD.
The easiest test you can do to have proof of this is: are you able to follow the localized and glide manually ? Are you getting the correct indications ? If yes, then you can be sure the scenery is fine, and if problems happens in auto-pilot only, they don't have anything to do with the scenery.