So, I was playing in UV, had a blue armor on and gothic boots with 13%hp as a marine and got one-shotted by an imp.
My max hp was 60, so 13% is at least 7 hp, max imp dmg is 10. Armor would reduce his damage to 0 (though I think you still take 1 dmg otherwise survivalist makes no sense).
In any case I shouldn't have died. This has happened to me before, but I assumed that I was being shot by something off screen that just wasn't rendering. Now I'm thinking that armor from boots or at least the gothic boots is not applying correctly. Or maybe it has to do with the type of damage (though on the wiki it says fire is reduced normally by armor).
Also, not a bug, but power mod in gothic boots is kind of broken (if the armor on them works right) 20 armor in an item that never degrades is ridiculous.