ok, I guess it's just a problem with how the elements are designed, they were given the flammable property, but not a property that changes them to fire when it gets really hot. I'm not sure if it's a bug, it's probably intended for some elements like these. I know other elements like WOOD still burn with only heat.
Temperatures are even higher now, and it's still not burning...
My proof being that I've gotten the DUST and THRM up to 6500 degrees without it burning or exploding or etc.