http://forums.worldofwarcraft.com/th...08205229&sid=1
8. “Impossible” simultaneous actions.
Examples: Rogue Vanish being broken by attacks, Two mages polymorphing each other, Paladin Divine Shield being dispelled as it is cast.
Because of the Client-Server nature of the game it is possible for two mutually exclusive actions to occur at the same time resulting in some unexpected behavior. Although efforts are made to minimize these situations they will still happen on occasion.
Also, are you stupid enough to think that the developers are the ones answering tickets? You send a ticket to a Game Master, they say "thanks", they close your ticket. Nothing else happens. Because they already know. And they don't need you to point it out to them.
Unless you feel like building a new internet with absolutely no latency and giving it to Blizzard to fix vanish, get over it.