Yeah, that's right, I don't know if anyone else has experienced it, but once in a while my Shadowfiend will just flip out and...not hit my target. I don't know what it does, but whatever it's doing, it's not meleeing the boss (I don't hear the mana gain sound and I don't gain mana) like on H Halfus tonight, when I used Sfiend I was at 30% mana, when it disappeared I was at 39%. No, I didn't have any int procs up. Yes, it's auto-set to aggressive.
I know, it only happens once in a while, but it's annoying to have your big mana return just flat out fail.