(Sorry about my english)
I had a K850i. It had the same problem. It is a nice cellphone but as far as I know SE doesn't know how to solve this problem at all. Mine was a new one and 6 months of using it I took it to maintenance because of this problem. Passed one month the send me back the phone saying it was a display fault :confused: and the problem did not occurred for another 6 months and then it came back. I repaired it again and sold it. But the problem is still there.