The usual way it goes with most mobs is this. Mob uses attack that would apply condition if it hits you. You use your shield. The mob hits you, but your shield absorbs the damage and survives. You don't take any damage. You don't get hit with a condition.
Unless the mob is a greaver. In that case, the same scenario plays out, except that you do get stuck with the condition, even though you take no damage from the original attack and your shield survives it. Is that a bug, or is there some reason for it?
The greaver itself isn't applying the status effect. The cloud it leaves behind when attacking (in tier 2 or 3) is what is applying the status effect, and you can't block it.