"Mana Shield" Skill Bug?

Hello all,

I noticed when I'm in a PvP match, occasionally when I use the "mana shield" skill, it uses the skill and I have to wait for it to cool down, but it doesn't actually cast the shield.
It's kind of hard for me to put into words, but the skill is used but doesn't do what it's supposed to do. (It just shields then disappears .5 seconds later)
Now, this hasn't happened recently, but it was happening not too long ago to me and a few other people that I know "IRL" that play.
Let me know if this is a bug, or intended, thanks.

Note - Nobody attacks me, or hits me for that matter.

P.S. - Sorry for double spacing, my space bar is all kinds of messed up.

I don't really know how. The only way for it to go out so fast is by using all your mana. But as you said, no one attacked you so no way. And i played pvp before and I can use mana shield tons of times. It should not be intented because you can use all your spells on pvp.

BOTTOMLINE : It is just a bug. It may have been fixed because it did not happen recently to you.