The patch has just arrived, and I tested warrior's Cunning. Warrior's Cunning applies the full +50% damage bonus to a target's health bar even if they only have a tiny amount of barrier.
Anet, I'm not sure how you managed to allow such a broken mechanic into this patch. RIP scrappers and anyone else unfortunate enough to recieve a small amount of barrier.
Please fix this by applying the +50% damage bonus only to the barrier. For example: If a target has 150 barrier, it will require damage 100 damage to destroy the barrier (100 * 1.5 = 150) and then any excess damage does not recieve the bonus +50% damage.