I just had an issue this morning, and I wonder if the GPS was the culprit...
I use my phone for my alarm every day, and this morning after I hit 'dismiss' my clock immediately changed from 5:30 to 4:30. I have no idea why this happened, it did not right itself until I rebooted the phone.
Now, for the past couple of days I have been leaving the GPS enabled, but in the past I always had it turned off unless I was using it. Would the GPS get out-of-whack over night, and affect the clock? I thought the time was pulled from the cell network, but who knows?