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I have this on my 4s. It's hardware, not software (already tried fresh install few times). Finally I used tweak (jailbroken) to override the switch because it already out of warranty. Sorry, not really exactly same with your case.
 
I'm not experiencing this on iOS 9.2 on my iPhone 6 Plus.

Perhaps try a restore.

If it continues it could be hardware related then check in with a Genius Bar at your most local  Store.
 
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