A question about your coffee maker overflow
been there, done that, but I have had occasion to take some of those things apart, and you would be shocked (pun intended) to see how crude they are inside. If it is/was still wet inside from the coffee getting down inside the base, you could have/had some leakage to ground from the hot inside. Can't guess the path, but worth checking. The timing is right as well. The microwave might be providing just the ground, and the voltage you are feeling is coming from some of that excess coffee/water in contact with a wire somewhere.
Bud