This is one of my biggest problems with this game. In my opinion, if a skill goes on cooldown then it should take effect. There is no logical reason that an instant cast ability should be allowed to be used but not take effect. I suffer this on Benediction when I play WHM. I also experienced the Hallowed Ground delay on Titan. I popped it, it was up on my buff bar for two whole seconds, and I still died to Mountain Buster. This is unacceptable. If it is on cooldown, it should have taken effect.

Incidentally, my fiance recently switched to WHM from SCH. She's incredibly frustrated coming from Lustrate over to Benediction, and it has caused a few wipes because Benediction's idea of instant is not the same as Lustrate's.