Far as I could tell there wasn't any hot water leaking in; no indication of wetness, no overflow. So it must have been acting as a thermos. Picking up heat during the previous 18 hours, and holding it when the room dropped from 85 to 70. Might have been some solar effect as well, because the sun comes in and hits the front of the washer in the late afternoon.
[This was really just an excuse to make a picture with Polistra and friends. I hadn't included them in a while and they were starting to get restless.]
The current icon shows Polistra using a Personal Equation Machine.