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.

talk.sonymobile.com/t5/Xperia-Z1/Xperia-Z1-Not-responding-to-power-button/td-p/438327
talk.sonymobile.com/t5/Xperia-Z1/my-sony-z1-power-button-wont-work/td-p/424501