The Surface power supply does not have a ground lead. So to drain off any static, it uses a balances drain resistor set to the power line. So if the unit is setting where it is insulated, it is setting at nearly 1/2 line voltage. On the US 120V system, you may actually measure over 50VAC on the chassis. On a Europe 230V system you may see over 100VAC with it floating.
Touch the cabinet, and it drains that away through you body. That slight current can look for a path through anything that is plugged in or touching the unit. Reversing the plug doesn't help because it is balanced.
Doesn't hurt a thing, because the current is so low, but it is a poor idea IMHO.