Master Yi Alpha Cleanse

So, this might not be a bug, but I was playing Nasus recently, and I withered a Master Yi while he was under turret, he alpha'd, and the wither was gone. The wither-alpha thing happened repeatedly, but it was particularly annoying at this point. I am not sure if this is a bug, but if it isn't then it should either be listed as part of the ability because hidden power of that level is bullshit.