While not Design per se its an interaction issue so i believe this is the place. The problem is that the UI works with only first touch on the screen and this creates issues (mainly with long reaches etc).
To explain -simply- whats wrong:
- Unlock your phone and put it on a flat surface
- Touch the screen with one finger and then use a finger of the other hand to touch the screen.
- Keep both on the screen.
- Move the second finger.
- Nothing happens.
- Move the first finger.
- The UI reacts.
Obviously the above isn’t a realistic scenario BUT as you hold/grip the phone and try to operate it with one hand is not uncommon to touch part of the screen with the lower part of your palm. And this makes the UI unresponsive.
So. Something has to be done about it.