First, the bug part: when destroying a crystal statue with a flaming flail I got the message "The crystal statue is burnt to death!" Since crystal statues are among those creatures classified as "unlife", this seems a bit off. I expect there is a similar problem with frozen weapons and with everburning torches. These messages should reflect the nature of the creature destroyed and the how of it, like "the crystal statue is shattered by the heat" or "the fire vortex is extinguished by your freezing weapon". It would require a number of messages given the different kinds of unlife but it would be less jarring and more flavorful.

Second, a tiny RFE: monsters leaving corpses after being killed with flaming weapons should sometimes leave cooked corpses. Just for fun.