Unused spells going on cooldown

Sometimes when I use a spell, it doesn't cast. It will make a sound and go to cooldown, but it doesn't cast. The reason this isn't me just placing blame is when I alt+click the spell, it appears 'Ready' in chat. This is a very frustrating bug considering the game's core activity involves spells. Please look into this...

I've had this happen with Amumu's ult and exhaust while playing Tryndamere.

Thanks