This has now happened to me twice, once on a control line plane and yesterday on a new R/C plane. After an very normal flight I let the plane rest for a few minutes then inserted a new battery and the ESC smoked on me. The only load on the ESC was the BEC. A very similar even happened when I was flying one of my C/L stunt planes, plug in the battery and instantly the smell of "Death Smoke". I would have thought that if anything was going to smoke it would be the MOSFETs that drive the motor, but in both cases the motor was not running or started. There appears to be a weakness in the front end of some of the less expensive (read cheap) ESCs. I replaced the burned one in my R/C plane with a new CC 36amp ESC, I hope it does better than the old one. It only had about 15 flights on it before taking a dive.