Possible Malzahar w bug on URF

I just noticed this bug because I main malz at support for a bit before he was nerfed. His w is acting like he was before he was nerfed though. Idk what it is, but his creeps do not slow down at all when they are away from him. And ik his creeps move faster when someone have the visions on them. However, multiple times I did not have them and I was rivers length away from malz yet his creeps were still running at me with full speed. Hopefully this was just a 1 time bug that wont pop up again