Any liquid on screen creates this problem for me with th Z2. It does not matter if its moister, sweat or rain drops they make the screen cray cray only way out is to wipe the screen.
This is exactly why I never wanted to give up my slide out keyboard phone. I wish more people were like me, I kept holding out for someone to make a respectable keyboard phone but I guess there's no market. I am not a fan of using the touch screen for entering text and numbers. Today was a prime example, my morning was rushed and I am fumbling to try an enter a new hires phone number. So frustrating, I swear it was the 15th try that I finally got it! Here I am fumbling with a phone while trying to direct workers to their tasks and deal with production and management at the same time.
I had this problem with my Z2, too.
Then, after an unlucky drop, my screen was broken, so I got the screen repaired. After approx. a week my screen got more and more its own life. At the end the phone was totally unuseable. The repair shop replaced the screen again, since then it just apperars from time to time like before.
I think Sony has some issues with these screens. My S2 which I had before the Sony had never such issues, even if the screen was quite dirty. Maybe thats why they introduced the Z3 so fast?
Here you can see the "amok screen". I enabled "Show touch" in the developer options.
https://www.youtube.com/watch?v=ocPnYQFqWao
Really strange, since I have never had that problem with my unit,
by the way, just for curiosity, how much have you paid for repair and where have you done it?
Paid for repair 225€ at a shop in Berlin. No official repair shop, in this case it would have been about 350€. However, it is no longer waterproof.
But they replaced the defective (ghost operated) screen without any questions at no cost.