#0 - Dec. 7, 2007, 8:16 p.m.
Blizzard Post
The developers have identified at least one issue with Cloak of Shadows and Vanish, which at times can cause these abilities to work incorrectly. These issues are under continued investigation and we will post more information as soon as it becomes available.

Please, remember that there are situations where Vanish can be broken by attacks due to client/server latency, this in an unfortunate limitation of our game and it will not change in the foreseeable future.