On numerous occasions there are time when I am casting spells I sometimes get interrupted for no reason.

The mob is right in front of me. I am not moving and it is not moving, but for some reason I get interrupted. I don't have paralyze or any negative ailment when I get this problem.

The only way I can describe it, is like trying to cast raise on a dead person who is disconnecting. You cast and the first half second it lets you start casting then stops and you get interruption message.

Is this a bug?