I’m inclined to question “is this a bug?” rather than assume “this must be a bug” – it’s fairly minor and doesn’t significantly impact battles involving this Troop, but regardless:
Troop: Herald of Chaos
Spell text: “Destroy a Row. Deal # damage to the first enemy and eliminate # points from a random Skill, boosted by Blue Gems destroyed.”
Naturally we assume that a spell’s effects should occur in the same order as phrased in the text, but as shown by the screenshot it is clearly the reverse: the stated damage is inflicted first, and any damage from Skulls contained in that row is inflicted second (passing on to a second target if the first target died).
By contrast, most spells that both destroy/explode gems and deal damage (e.g. Possessed Urska, Volthrenax) will deal damage after the destroy/explode is resolved, which has a convenient side effect of being able to de-barrier/de-reflect the first opponent before striking. Possessed Urska specifically is a great comparison because its spell also targets the first enemy, where it is easily observed that any destroy/explode damage occurs before the main spell damage.
And this may be related to a larger issue where spelltext on many troops doesn’t seem to match the actual order of effects – e.g. Spiritdancer summons a troop before converting a mana color to Green (allowing said troop to collect Green Mana) and Amira steals 2 Magic before dealing True Damage (thus boosting the damage by up to +2). BUT on the other hand, I can speculate a consistent intent behind this being common: Spells that involve user interaction (e.g. select an enemy, ally, or gem on the board) generally state this interaction first regardless of whether or not it is actually the first effect processed when the spell is cast, and this seems actually important for the user to know first. After all, you don’t see spells that execute partially THEN pause for user input before executing the rest.