I created a base file (~50BG) in February and have since made 3 differential backups. The first two are small (~1MB) and were made in February. The third backup is larger than the base file (53GB) and was made in April. However, I have definitely not changed all of the 175GB that I'm backing up. I've probably only changed ~10GB at most. I noticed in the progress box that it was compressing files that I have definitely not altered, moved or accessed.
Is this behaviour expected? If not, (taking a complete stab in the dark) it wouldn't be a bug that has anything to do with daylight savings, would it?