Prior to Update 11, this skill was named "Robust", and had no effect on healing received. It was renamed Unflinching, had its HealthRecovery reduced, and added Healing Received.
In Update 21 the skill was renamed Unflinching Rage. It was changed to grant MaxHealth, the Healing Received was removed, and a heal was added that procs from weapon attacks.
In Update 29, the heal was changed to proc from dealing damage, rather than requiring a weapon attack. The heal amount was increased, but it can no longer Critically Strike.
Robust: This passive ability has been renamed to "Unflinching." It now increases your Health Recovery by 6/13/20%, down from 10/20/30% and your healing received by 1/3/5%.
Unflinching: Increases Healing Received by 5% and 20% Health Recovery → Unflinching Rage: Grants 1000 Max Health and heals you for up to 600 when you deal damage with a weapon, with a 4 second cooldown.
This passive now heals for 2125 Health when you deal damage once every 4 seconds, rather than healing for 600 Health when you deal damage with a Weapon Attack once every 4 seconds.
Fixed an issue where this passive was not considered a proc.
The heal from this passive can no longer Critically Strike.