…an old adage of wise mechanics. When something suddenly stops working consider what you were last doing. 

My iPhone touchpad started typing on its own. :(. I asked the Internet and no help. Thinking back I realized I had been working on tractor just before it started misbehaving. I had hydraulic oil on my hands (probably) and contaminated screen. I cleaned the home button and problem went away. 

….where were your hands last.