Like tittle says, /cancelaura Dispersion command & macro doesn’t work in most cases.
Here a post talking more about the issue: https://www.reddit.com/r/classicwow/comments/1ap8tcr/cancel_dispersion_macro_not_working_sod/
Common Blizz. We are paying 15 dollars for month for a hard bugged game. This kind of bugs mess all in PvE & PvP situations.