Confused about the Vanish skill.

[incupal2 0]

I'm playing with a pikeman class char and I find its Vanish skill confusing. I thought this is supposed to make you invisible until either the time runs out or you start attacking. However, I tried using it a couple of times and the monsters are still attacking me when I walk by (even though I'm not hitting anything). Can you guys enlighten me on how this skill really works? Thanks a lot!

[DarkLink64 921]

Vanish reduces monster sight range by 90%.

 

This means if you're too close, they'll still attack you.