Oh you were talking about vanish then? because it says damage and harmful effects received will not break it for 3 seconds. Nothing about not breaking when you open, so I really am lost as to what tooltip you are talking about.
i misread, your'e correct.
After testing some more:
When talented for subterfuge:
On vanish and sprint->vanish, buff counts down AFTER improved vanish buff ends. On opener, when attacking from stealth, buff starts counting down upon attacking
When not talented for subterfuge:
Buff begins on attack no matter if opening from stealth, vanish, or sprint->vanish.
It's inconsistent when talented for subterfuge, it behaves as if it should work for subterfuge, but doesn't. As if they attached the countdown initiator to the wrong trigger.
It does behave consistently when not talented for subterfuge.
It might be worth reporting as a bug. Either it's supposed to work with subterfuge, or it isnt, i'd like some clarification from blizz