Champs that keep their stacks are r*tarded.
While I dont care that champs are allowed to keep their stacks, its dumb for the amount of damage they deal vs the amount of mana they use.
Nas at 1000Q is allow to hit you forever since it takes not mana at all. The mana should balance out via damage. Example: 10Q -(few mana) and 1000Q - (more mana). This way Nas is only allow to hit you a few times or kill one or two champs and NOT THE WHOLE TEAM.
This rule should apply to all champs that stacks (expt cho, he max out at 6)