Odd problem with my otherwise working W600

Hello,

I have a Sony Ericsson Walkman W600. I love the phone, and have never had a problem with it. However, yesterday, something strange started happening.

Basically, the phone isn't registering when I have an outgoing or incoming call from a number within my contacts. For example, if I receive a call from "ICE 2", instead of saying "ICE 2 calling", the number associated with that contact comes up instead.

If I call a contact by scrolling through my contacts and selecting it, it comes up during the call as "calling contact X", but, in the history, it just shows the number I called, and not the contact.

If I look at my call history, it's spattered with (and seems to have no pattern) with some calls being attributed to a contact, and others just attributed to the number associated with a contact.

Nothing out of the ordinary happened the day before the problem began, aside from my incoming call ringtone expiring. Perhaps this had something to do with it? Maybe not. I'm just sort of at a loss.

The phone is otherwise awesome, and I love it, but this is just sort of annoying. Is there a known fix for this problem, or do I just need to live with it?

Thanks very much in advance for any help!