It gets hotter while plugged in due to the fast charging. This charging method generates a lot more heat than previous generation surface devices.
It's also important to keep in mind the body is made of magnesium. It was made of this material to absorb the heat from the CPU. So the body acts as kind of a large heatsink. This is normal but shouldn't result in an unresponsive touch screen. More than likely the driver was updating. That would also explain the audible "disconnect" notification.
I recommend ensuring the device is fully updated, then runs some personal tests on the device to see how it functions. I hope this helps.