Rammus E goes on random cool downs.

Very easily replicable.

Have target outside of brush you have vision in. Be close enough to taunt. Let target run in to the brush, taunting right before he gets in.

Each and every time, it will put the e on "cool down", even though nothing happens. You can ping it, and the game says it's available. But it won't let you use it again, until you wait the full duration.