Thank you for posting to the forum regarding you question about call history. The call history is heavily tied to your mobile operator. This update issue you are seeing may be related to issues on the providers network. Before we settle on this there are a few things we should try on the phone.
Check the call history carefully to make sure that old and new calls are not being merged. Often times the call histories of a contact will be put together, be sure that the new and old calls are not showing up in the same string.
Go to the phone and tap settings > applications > Internet Explorer > delete history. After you do this, go to settings > emails + accounts > tap and hold the Windows Live account and select sync.
If you continue to have this issue try performing a soft reset of the phone. The easiest way to do this is to pull the battery for 2 minutes, replace and restart the phone. If you are unable to remove the battery, consult your owner's manual or contact your phone manufacturer.
If you are unable to make progress with all of the above, contact your mobile operator to inquire why all calls are not being track or added to your call history.