Fiora's w cancels all of your commands?

Just played a game as shen vs fiora and for some reason everytime she w's my auto cancels even though i never used my e or any form of cc. Its almost like her w slows my attack speed by like 50%. Also, when she uses her w while I'm walking, i stop walking. i know fiora's w is meant to give her immunity for a short while but it feels like her w actually stuns you momentarily with no cc blocked or maybe resets all my action commands (auto attacking, moving, using skills, etc).