Bunker doors have an overheat temp of 1200C, however they will not take overheat damage unless you open/close them when they are above that temp. Also if they are taking overheat damage they will not stop taking it until they go below 1200C AND open/close. So effectively they cannot overheat or stop overheating until they experience a state change.
Steps to Reproduce
Place bunker door, heat to 1200C+, it will not take overheat damage, start opening the door, it will start taking overheat damage. Close door again and cool it off below 1200C it will still continue to take overheat damage, start opening the door it will stop taking overheat damage.
This issue has not been confirmed by a developer yet.