Targetable Stealthed Teemo Shrooms?

So I in my last game I was going ward crazy because I like vision and it was my first time mid, but it seems to me that for some reason when I put my cursor for my Ward over a spot where the enemy Teemo placed a shroom it would turn red. It did not seem to do this anywhere except where I KNOW the shrooms were(due to their repetive placing, and running into the spot on accident to get a surprise.) Generally the I only noticed this when they put the shrooms in bushes, but those were the only places I was placing the wards that the Teemo was placing the shrooms.

I know I hate Teemo, and more specificly the shrooms: But I thought I should at least get this out there.