Cassiopeia's passive stacks constantly [Gameplay]

I'm pretty sure that Cassiopeia's passive isn't suppose to stack constantly, so correct me if I'm wrong. Cassiopeia's passive keeps gaining one stack every 2 or 3 seconds. It does not matter if the player dies or not, Cassiopeia will continue to gain stacks on her passive. This happened to me every single game I've been in with Cassiopeia. I know for sure that this happens on summoners rift, but not on any other maps.