Kinda annoying seems like something that should be fixed in an upcoming update. Just had a Garen go top and totally ignore the enemy and smack towers for massive chunks of damage. Same with Zed, he can also exploit this. Hopefully this can be fixed soon. If you don't know what I am talking about well with the new runes there is a run under the "Sorcery" category called "Transcendence" giving you 10% CDR at Level 10, but it also states that when you pass the CDR limit it takes the excess CDR and adapts it into AP and/or AD so if you stack black cleavers with it you not only have max CDR, but you become super tanky thanks to the HP that black cleaver provides and also do CHUNKS of damage!
TL;DR Lots of black cleavers + Transcendence = bad game and rage quits lol