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Are you sure they are rolling over? If you are confused by having calories tracked when you get up in the morning this could just be your BMR calories.
As well as tracking calories burned through activity your fitbit also tracks your BMR calories. These are the calories you burn just keeping your body alive (even when asleep). They are calculated from your profile settings for age, height, weight etc so you needn't be wearing your fitbit to get them. What you are seeing includes the total BMR calories burned since midnight.