1982’s Doctor Strange #53 (by Roger Stern, Marshall Rogers and Terry Austin), Doctor Strange (looking for the past selves of Morganna Blessing to find her lost soul) ends up in the same time period as the Fantastic Four, where he is knocked out and captured. He left his body and traveled to the astral plane, where he then encountered the Fantastic Four’s journey that we saw before, only now we see that Strange had an effect on their adventure, specifically on the Thing's transformation...
Amusingly enough, later the West Coast Avengers would travel in time ALSO to that same spot!
But anyhow, so there you go. It was not actually the heat that changed Ben, but Doctor Strange's spell. That would explain why heat never had that effect again.
Thanks for the suggestion, Rob!
If anyone else has a suggestion for a future Abandoned Love, drop me a line at email@example.com!