I recently got a Sony Xperia Z1s from T-Mobile here in the states. Despite the slightly dull screen, it was my favorite of the available phones. Unfortunately, the phone I got as well as the one my girlfriend got have an intermittent touch screen issue. In attempting to research and troubleshoot it, I was able to confirm that it is an ongoing issue, that Sony knows about it, and that a fix is due in an upcoming firmware update. Unfortunately, Sony does not yet have a release date for the update.
What Is The Intermittent Touch Screen Issue?
The touch screen on many Sony Xperia Z1/Z1s phones will sometimes cut out during swipes or holds. This results in a continuous swipe or hold being interpreted as a release and a click. If you're scrolling in a web page, the page will stop scrolling and whatever link or ad is under your finger will be clicked. If you're using the on-screen keyboard and holding to get a number from the top row, you may wind up with a letter instead. And forget about attempting to swipe type using the Google Keyboard or Swype. You can test if your phone is affected using the built in troubleshooter by going to About Phone and then Troubleshooting and then Touch Screen from within the Settings app. Here is what an affected phone looks like (the issue presents itself about 20 seconds in):
(The video has since been removed from YouTube)
Possible Causes and Reports
A number of people have theorized that it could be due to the touch screen shorting as you make contact with both the screen and the aluminum bezel. Or that it could be another finger in contact with the edge of the screen. Others have theorized the opposite. From other reports, it happens both with and without a bumper style case. There are 41 pages on the issue at XDA Developers and another 43 pages of discussion on the Sony Mobile forum.
Confirmation and Upcoming Fix
On page 29 of the Sony Mobile forum topic, in a post from January, a Sony representative named Rickard states that:
I just got news that there will be a fix for the touch screen in the next software update that should solve this.
I called Sony on March 4th about the issue and they confirmed the issue and that a fix would be coming as part of the Android Kitkat 4.4 update for the phone. Unfortunately, they could not provide a timeframe as to when it would be released. They also reminded me that it would take additional time for the mobile providers (T-Mobile, Rogers, etc) to then roll out the update.
What You Can Do Now
Unfortunately, there's not a whole lot you can do. You could try adding a bumper case (or taking it off) to see if that changes the way your phone performs. Several people who sent their phones in for warranty service reported simply getting it back with a message that there was no problems found. Others who attempted to exchange the phone at the local shop they bought it at reported that many of the phones they tried also had the issue, so it could be affecting entire batches shipped to specific stores. I wound up returning both my and my girlfriend's phones and getting Galaxy S4s instead, the only other high end phone T-Mobile has with microSD support, also as part of the $0 down program. It's up to you if you wish to return it for another phone and you're within the return period or wait until the future Sony fix. If you're outside of the return period, you're either stuck waiting or selling it and buying another phone.
I'll update this page if I get more information...
Update, April 2, 2014: Kitkat Released Without Fix, Possible Root Fix
The 4.4.2 Kitkat release has started hitting Sony Z1 and Z1s phones for some carriers. Several users have reported that the internmittent touchscreen issue is still present in the new 14.3.A.0.681 firmware release. So, it would appear that Sony has not fixed the issue.
A thread over at XDA offers up a possible fix if you root the device and reset the touch screen calibration configuration. I no longer have a Z1s so can not comment on its effectiveness beyond pointing folks to the responses listed in the thread.