I've had many issues where people can stun or CC me through a vanish- either the detarget doesn't work, or some kind of latency bug kicks in. We also have the situation where you get to close to someone and it takes FOREVER for them to detarget you, but that's not related to vanish (probably).
What Holo says is correct- vanish gives you a 3 second "blessed" period. I don't think it's possible to be knocked out faster than that. I bet what happens to the poster claiming otherwise is that he's vanished, but still being attacked, and doesn't realize he's hidden.
sooo ...FW debuff halfed, pvp power halfed. base resil 65% ...well I'm curious how this will play out. I bet there wont be any base dmg buffs for sub rogues