iPhone 4 SMS Timestamp Issue

Hi,

I have never had any problems with my SMS timestamps but all the messages I am receiving today are displaying the wrong ones. For example with one person I was texting, the timestamp in the main inbox was coming up as 'yesterday' when we had been sending messages to eachother this afternoon. I deleted all the messages that I got from her 'yesterday' and a new timestamp appeared and it was the time of the first message I received off her today.....no matter how many texts to and from we send it wont update. I'v made sure all the time/date settings of the phone are right and even restored it in the hope of fixing it. If anyone could shed some light on this it would be a great help, it's driving me absolutely crazy!

Thanks!