I have exactly the same problem with my Sony Xperia Z3 Dual that I bought today 1 year ago.
I got a new screen 4-5 months ago as warranty to repair this problem and now it is coming back again. Seems to me that there is a mistake in the design somehow if it appears again in the same way
I googled and I didn't find anything particular about it, apart from changing the screen with the warranty and doesn't look like a common issue for many.
As my warranty expires today most probably I cannot do this trick again and even if I do how can I make sure it doesn't come back again?
Has anyone any idea of this problem? What causes it?
