Sorry if this is very long and boring, but saying it all now saves everyone from saying it later
There is a massive problem that the Z1 suffers from, an erratic touch screen.
Some people have the problem, whilst others don't. I am one of the unlucky owners of a Z1 which has this problem
People report that the screen registers an input, then shortly losses the input and then regains it, making web browsing difficult as anything you scroll by could be clicked by accident.
I suffer from that and then some. If I use the phone for a prolonged period of time (usually 20 minutes), the screen will register my input at completely different places to where my finger actually is!
This makes normal use almost impossible since you have no control as to where it will register your input.
Oddly enough, locking the phone for a few seconds (just long enough so that the phone falls into deep sleep) then waking it again makes the problem disappear temporarily. It does start doing it again eventually. This happens regardless of phone temperature. This also proves that the issue isn't hardware related, as if it was then it should be doing this all the time, regardless of anything.
Trying to do a clean install fails to fix the issue (at least for me), and even the highly anticipated KitKat update failed to address the issue, despite them claiming that KitKat will fix it (it didn't work for me).
NOW comes the possible solution. Since I know that this could not be a hardware issue, there must be a way to fix it via the software.
I researched a lot and found something that could fix the issue.
I'm saying this now. I don't guarantee that this will fix the problem, but trying won't hurt anyone
I didn't do a nandroid backup (I'm on 4.4.2 = no system mount in recovery), but if you feel uncomfortable with this, then by all means make one
You will need the following:
Any file explorer with root access
External microSD Card
Any stock/stock based Sony ROM (try the fix on other custom ROMS if you want. No harm in trying, cough NANDROID IS YOUR FRIEND )
1: Open up the Terminal Emulator
2: Type in "su" with no inverted commas.
3: Type in the following command: touch /sdcard1/Calibration.ini
There must be a space between "touch" and "/".
If done right, you should get no response (no message at all, just back to "root@C69XX:/ #"
4: Enter and after that, shutdown the phone. Whilst it is booting, do not touch the screen. You can safely touch the screen after it is done booting (when you can see the UI). You can also reboot it instead of shutting it down, but I found that a proper shutdown works better (your mileage may very).
5: Goto a file explorer and delete the "Calibration.ini" file. This will prevent the phone from calibrating the screen after every reboot (not needed since it has just been calibrated).
6: All done
Now, test the phone properly and see if the problem is gone.
If you have the time and patience, I recommend setting the screen timeout to 30 minutes and using the phone without letting the screen turn off. If it doesn't do anything strange in that time, then you can safely assume that the problem is gone for good
Ever since I did this, the problem has ceased to be. It has gone and met its maker
Hopefully you will have the same results
Even if it didn't work, there was no harm in trying
Note: For the app that does the same thing as this method, see post #2