My microwave is ungrounded because the EU is terrible at standardising plugs and sockets. The microwave would be grounded if it was plugged into a schuko socket (CEE 7/3), but instead it's plugged into a socket with no earthing clips. The microwave is leaking current though the shell, and gives you quite a shock when you touching a ground (I.e. the sink). It feels akin to a static shock, but continuous.

Tomorrow I'll buy a volt meter (and a new microwave) and test how much current is leaking.