This seems fair enough, tbh. If a Barrier is supposed to block the triggering of a Deathmark (which it does), it’s a bit weird that you still lose all of your Armor.
To clarify, I can confirm from previous experience that this is the behaviour that occurs when Deathmark triggers on a Barriered troop (Armor → 0, Barrier removed, Deathmark remains).
I imagine this is because stripping Armor (e.g. Rope Dart) doesn’t count as damage, currently, while damage to Life would, and Deathmark is probably coded to do both (just speculation, though).
Maybe an easy way to ‘fix’ this (depending on what’s intended) would be to remove the Armor stripping part from Deathmark (if that’s a thing) and just have the damage to Life (as a Troop will still die at 0 Life even if it has 1000 Armor). Then Barrier would still block the triggering of a Deathmark without having all Armor removed.