Warrior: Chest Splitter question

[TritonForge]

I've spec'd 2 points into Chest Splitter, into Staggering Blow, with the intention of mapping it before boss fights.

I just tested it out on Bloodhammer, and activated the skill when I saw a red area of effect indictator. But, his attack went through anyway and every attack that gave a red area indicator proceeded regardless of my chest splitter. Even when I winded/charged it up and released before the attack executed the boss' attack was not interrupted.

Can someone explain how I'm doing it wrong? Does the red area indicator mean the attack was already wound up and I have to interrupt an attack before that even shows? Does the interrupt on Chest Splitter not work on bosses?

Thanks

[Thermite]

I believe STS changed the skill a few updates ago so that it no longer interrupts the wind up of a boss.

[Rollo]

Doesn't work on most bosses, which seems like a big short coming for a tanks tool kit in my opinion.