Diana bug with W.

I have been playing Diana a lot recently, as she is my main, and I have noticed 3 times now a glitch regarding her W. It's happened 1 time per day, consecutively for the past 3 days. The first two times I thought it was just in my head or maybe it was just an animation bug. But in my most previous game I clearly witnessed casting my W, Diana doing the animation as she normally does when casts her W, but there was no spell. It charged me the mana and it put the spell on CD ~1 second after trying to use the spell. Has anyone else heard or seen this happen recently? If it is a real glitch I think it should be fixed immediately. I died in a one-on-one duel because there was no shield. Or so it seemed.