w910 address book names not showing when receiving call

I purchased a w910 about a week ago and I just noticed that when I receive a call from a number in my address book, the name of the person does not show up... simply the plain number.

Is this a bug, or do I need to do something to enable this functionality?

I synced my address book with my mac using a iSync plugin.

Check SIM and Phone contacts numbers. May be you have SIM number in Phone contacts and when change something in Phone you have AutoCopy on SIM and you have same person with 2 different numbers.
Sorry for my bad english.

try reset the phone