I edited my original comment.
My situation is not atypical and my lag is not bad (15 ms ping to the server) Upload a video of yourself instantly (or at least within a reasonable amount of time) cancelling casts by moving. I would absolutely love to see it. I've been playing since the 2nd beta phase, this issue of movement lag has been around since then and despite tons of people claiming that it is non-existant I have never seen one video that proves that this issue is client-side. I've played this game with tons of people on tons of different ISPs and the issue has persisted every time.