I also had this problem last night when landing my spaceplane. I was returning from <90km orbit and at around 60km, everything started to overheat, including my Big-S delta wing. My medium landing gear almost exploded. This should not be the case. I'm going to check the buglist when I get home this evening and if it hasn't been added, I'll take screenshots of the same plane reentering at Kerbin, Eve, Laythe, & Duna using 1.7 vs. 1.8 and add it as a bug.