Edit: Still bugged for bugged for 288927 which introduced even higher temperature materials and the ability to make buildings out of raw ore with the new refined materials.
See this thread:
Apparently, the code that actively deletes heat around an over-heating building resets to the building's base over-heating temperature -after- reloading the game/save. Not the building's boosted over-heating temperature from the material it's built from.
Steps to Reproduce
This works for at least the AETN, but have it actively near it's over-heat temperature so the code is deleting heat around it then, upon save/quit/reload it immediately reduces the temp around it and the AETN to 75C, then stays that way as you run the game. This happens on any building producing heat.
This issue has been fixed in either a future version or updated in a previous version.