This protector behind is in case you break the glass to not hurt you....
It's your Z1 come out from box with the back protector? Because far as I know they don't...and mine didn't have it.
IF I HELPED DO NOT SAY THANKS, CLICK IT. My Evolution: Sony Xperia Z1 - UB + 4.3 Rooted + Deodexed, HTC HD2, HTC Diamond 2, HTC HD Blackstone, Nokia 7070 Prism, Qtek 9100, Nokia 3100, Motorola T720i, Nokia 3310, Sony Ericson PF 768 (Blue)
How Get Root on Sony Xperia Z1 with Locked Bootloader and the Latest Android 4.4
If you watch this YouTube clip. There is actually a square heatshield for a chip in that region behind the back cover. Maybe that would cause it. I don't know if my eyes tricked me but it looked like his back cover also had that square.
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