I think I know what you're getting at but I probably don't have the answer you'd like. I noticed the same issue and I think it has something to do with weather or not you stored the contacts # with or without the area code.
I recieved a call from one of my contacts the other day but their name didn't show up, only the # with area code. I checked their contact info and, sure enough, I had entered their # without the area code. I'm thinking that is what caused the phone to have not recognized the contact.
Maybe someone else will know more...