Bob: This is an interesting event. There is always a logical explanation for all effects of electricity. Unfortunately, I do not have an immediate answer, or possibly no answer.
I will investigate the power supplies of micro-wave ovens. I think they present a non linear load. This can produce a distorted sine wave. I will also look at frequencies this produces, and see if there can be some relationship with the sensing system of the other non related device.
Keep us informed if you discover a more sensible resolution, or cause.
