Void Staff Item Description (Is it a nerf?)

So Void Staff's description used to say "Ignores 35% of Magic Resist" or something like that. Nowadays it says that it gives +35% Magic Penetration. So that would imply that it would increase your flat magic pen by 35%. Rather than ignoring 35% of opponent magic resist. So basically, if you have a low amount of flat magic pen, if any at all, void staff would basically be giving you only the 80 ap. Correct me if I'm wrong on this, but that is what it seems like.