This will make several of the quests harder... but then I've already finished them. Solid Wood isn't triggering on non-fire attacks after I use a fire attack against an enemy holding that armor. The armor stops triggering as soon as I attack with fire, but could possibly be due to having a burn effect attached - I've always managed to kill the enemy before the burn effect wears off.
Er, actually, another symptom I just noticed - beginning-of-turn acid effects ("discard armor") don't cause Solid Wood to be discarded when it gets into this state.
Er... my bad. Looking over the screenshots, I just realized that I was only confused about which enemy had the armor attached. (Is there any way to delete this thread to save some small shred of dignity...? )