Around 40 some years ago, I remember my mother saying she did not like coffee heated in a microwave because it didn't stay hot. I didn't pay much attention as I didn't drink coffee then. I noticed the same thing a few years ago. Then I decided the coffee was stratifying in the cup while being nuked. Hotter on top, cooler on bottom. So I got in the habit of giving it a quick stir after nuking. Tonight, I heated a cup of water and thought, "Why don't I check." I stuck in the meat thermometer. 165°F near top and 122°F near the bottom. Mystery solved. Probably going to check this again some time just to be sure.