Alistar ultimate teemo counter [BUG]

I moused over my w to check its range as Alistar, and i noticed a spot where i could knock something back. at first i thought it was a bug that showed the direction of the last champion you spotted. Then i thought what if its Teemo invis right there, so i walked over to knock him up to step on a shroom. Albeit it doesn't ALWAYS work, but for the most part you have a permanent sweeper lens as long as you are mousing over your w when looking for shrooms. (It only shows you the location not the actual shroom)