Identical usage\standby accumulator statistics

​I've recently bought a new iPhone 6S (128 GB, Samsung A9, iOS 9.2.1 from box ) and have configured it with my 4S iCloud backup copy (data and settings). I've noticed that if I charge my iPhone to 90%+ (the battery level where it resets the battery statistics to 0 after disconnection from charging) it often begins to count the standby time and the usage time in accumulator statistic minute-to-minute. I mean the behavior of "usage time" becomes the same as "standby time". In this situation the battery doesn't drop abnormally or any other way than usual. (For example 6-7 hours of night standby with GSM signal turned ON, gives just -2-3%). I found that I need to turn iPhone off and than to turn it on to fix it. I mean, it's not a huge problem, but I'd like to know if someone encounters the same thing? I heard it could be provoked by the backup configuration, but I'm not sure. Can someone help me with any advice or experience?