Sony Xperia Z1S is having touchscreen issues.
Buyers beware!
I've already gone through 5 of them. Two of them in store with the customer service reps witnessing the issue fresh out the box. Just an FYI!
No solution ->> Xperia Z1 touch screen problem - xda-developers
Towards the back of the thread, you'll find many complaints of the Z1S http://talk.sonymobile.com/t5/Xperia-Z1-Z1-Compact/xperia-z1-touchscreen-problems/td-p/410611
How to determine if you have issues. After you've been using the phone for approximately 5 minutes Go to Settings > About Phone > Diagnostics > Test Device > Touchscreen. Then draw on the screen without lifting your finger for the 10 seconds it allows. If the line is continuous for those ten seconds, you may be okay, but I recommend you trying it again if you notice any oddities. However if the line disappears then your touchscreen is messed up.
Sony Xperia Z1 touchscreen problem - YouTube
Let's hope this issue gets under control