No es bug, de hecho, es como tiene que funcionar, no debería atravesar inmunidades completas como Divine Shield o Ice Block.

De la página de wowwiki:

"...It even ignores damage reduction effects like Pain Suppression, and critical strike damage reduction from Resilience. Note, however, that this does NOT penetrate full immunities such as Divine Shield and Ice Block."
Igual está bueno

Saludos