Counters go off in the way they get activated, except when Veteran Paladin uses his Skill "Smite". (Atk+30 to target enemy, HP-30 to yourself) You always see the damage inflicted upon yourself being calculated first, and then the inflicted dmg on your opponent.
In my case Veteran Paladin had 40HP, calculated i could:
Target Guardian > Do -30 HP to myself > Dmg her for 60(-10Def) > Heal from my Paladin's Counter > Tank Guardian counter.
Instead Guardian's counter goes off first dispite being (visually) calculated later. Killing my Paladin in the process.
This happened before and perhaps it's intended, but it just looks so very illogical. You easily are stuck in the basic thoughtprocess of calculating&predicting your remaining HP (as you always do), and heal when it'll get below 20. This game becomes needlesly complicated if we suddenly see exceptions for certain cards to -what once were- basic ground rules.