Thank you for your reply.
I tried reinstalling firmware via PC Companion and it didn't help... I was afraid flashing the phone might void the warranty... Does it?
Here is a picture: (not nice quality, sry)
(the area below soft keys is missing...)
A few more things to mention:
* When I take a screenshot, everything is fine and the area below the soft keys isn't missing!
* At the first days, the missing area was appeared when phone was heaten a bit... But now (for about a week) the area is permanently missing!
It's much like hardware problem, I guess.
Sent from my Xperia Z1 using Tapatalk