I would tend to think if an original file and its backed up sibling are exactly out of synch by 1 hour (or multiples thereof) the reason they are out of synch is very probably because;
1. Daylight saving has kicked in or out
2. Or you have crossed a time zone and updated you computer time to the prevailing local time by exactly n hours. International time zones are nearly always in hour intervals except I think in a couple of Pacific Island groups using 1/2 hour.