Fiddlesticks Terrify bug

Has anyone else noticed that on occasion, using Terrify puts it on cooldown, but has no effect on the enemy champion? I've been playing fiddlesticks a lot the past few days and this has happened on at least 4 seperate occasions. What is the cast time? Is it possible I die in the split second it is casting, therefore canceling it, putting it on cooldown, but not actually affecting the target?