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.
Branch: Preview Branch