Missed calls log missing

It happens to some Cisco IP phones that missed calls log become empty. It is a weird situation and it may confuse the end users. You may see this behavior in ccm 7.x version. The problem won't go away even if you reset the firmware to default version and then upgrade to the latest version. The best solution is to remove the phone device and directory number from the data base. make a search that directory number does not exist in call manager. Then create the phone and assign the directory number to the phone.