Problems using a capacitive touchscreen whilst charging

Yesterday whilst travelling by train, I decided to charge my phone at one of the power sockets provided in the railway coach. As the journey was long, the phone battery wouldn't have survived all throughout the travel, moreover because the railway route was full of patchy mobile signal. During the time when it was connected to the power supply, I noticed that I was just not able to use the touch screen. I tried hard to swipe my finger to unlock the phone, all in vain. So, when I gave up trying to operate it, I observed things moving on their own on the screen, I could see the camera starting automatically. Out if curiosity, I just unplugged the charger cable and everything was back to normal.

Capacitive touch screens use a layer of capacitive material to hold an electrical charge; touching the screen with your finger changes the amount of charge at that specific point of contact. But, capacitive touch screens won't work if you are wearing gloves or if you try to operate it using any other insulating material. Also, an important requirement is proper grounding for the touch screen sensors to sense the variations in the capacitance along the screen.

Now, if you use a power socket, which is not properly grounded, to charge your device, you can very well expect the touch screen to behave funny. This would happen very often in the power sockets provided in the Indian Railways' coaches. Also, it's very much possible with a Car charger, since both these places would most of the time not be grounded properly.

Specially operating the touch screen whilst charging in railway coaches or cars could make it behave funny if the electrical system is not grounded correctly. The change in behaviour of the touch screen should not be permanent, it will come back to normal once you unplug it from the power socket.

Sometimes, you might get a tingling sensation in your finger when you try to operate these touch screens at such places. While under normal operation of a capacitive touch screen, your finger collects some static from the screen, the effect is even more while charging the devices at places without proper grounding. Again, this disappears the moment you unplug your device from the power socket.