Default Power button does not respond properly.

I purchased my C6902 a week ago. I updated the phone through flashtool to 14.2.0.A.290. after which whenever I push the power button, most times it would switch on to the unlock screen but sometimes I have to press it multiple times. But it would always get locked the first time, every time I pressed the power button. I tried a factory reset and the problem still persists. Anyone else facing it? A few other owners are also facing the exact same problem.