Sony Ericsson Z520 / Z525

Hi there, I just got this phone not too long ago and I love it, except i've been putting in different appointments in my calender and it seems that after a few days or whatever it automatically changes the time that i originally set it for. If i set one for 1-2 PM it'll change to 10:45 PM to 11:45 PM or something like that, any idea why this is happening? I tried to disable the auto-update for the time, but I dont think it did anything.