The spec_heat of blood makes it wonderful insulation. Get a couple of types of blood coating a wooden item, or a cloth shirt, etc, and it will last an impressively long time in magma. It easily outlasts things like copper and silver (unless they're blood-coated as well, of course). You can burn bloody cloth/wood while not melting copper (say, in a quantum-stockpile of invader droppings) by doing a slow heating (one 7/7 magma tile in a system that pumps magma onto the tile, lets it drop a couple z-levels, and then it gets caught by the pumps to restart the sequence), though even then it's easy to overdo it. This also means having a bloody mess of weapon traps in front of your magma-traps winds up providing invaders with a fresh coating of anti-magma insulation ><
I haven't poked around the dwarf materials to be sure, but I suspect that this is the cause behind the way the dwarves die - the fat layers are first heat-accessible layer to reach a failure point (by virtue of their spec_heat, failure temperature, and construction of the body), leading to mass bleeding. The blood would take much longer to heat up, and thus likely the dwarf is dead before the blood has reached boiling - also keeping anything thermally protected by blood from becoming vulnerable in any practical scenario. Overall, very little in this version seems to !!burn!! - stuff gets destroyed by flame certainly, but very little of it seems to !!ignite!! before getting worn down to destruction, at least for me.
Also, it seems that 'burning' (!!stuff!!) and 'fire' (the "a fire" object seen on burning grass tiles) are treated differently. Fire seems to be able to destroy contaminated cloth, leather, and wood items much more easily and quickly than 1/7-3/7 magma. !!Burning!! objects seem to follow the same rules as magma does, but 'a fire' seems to use a different system.