Timing reset of Nokia 2760 | Phone/Device Issues and Features | Consumer forum

I got a 2760 during last promotion. But this phone's time and date information were lost each time I opened the battery cover to switch the sim card to my older phone 1112. So I have to correct the time and date each time. Is this a bug?
I got another 2760 with Petro Canada. That one doesn't have this problem.