Teemo mushrooms with a huge trigger radius?

I recently played a game against Teemo, and my team and I were getting wrecked by his shrooms. I don't mean by walking into them, either.

I was playing Miss Fortune and was not able to auto attack shrooms from max range without them exploding on me. I am 100% sure about being max auto attack range away from them. I have played against tons of Teemos before without having this kind of issue. Can anyone please tell me if they've experienced anything similar?