I have the same problem. I just updated my Xperia Z to the latest update (4.2.2 Jellybean, firmware 10.3.A.0.423), and decided to try talkback. The phone immediately became sluggish and unresponsive, and I am now unable to scroll. This means I can't disable the feature from the settings menu. Every menu item is highlighted with a box, and accompanied by a vibration. I have tried restarting the phone with no success, so I'm now in the process of repairing the phone using PC companion.