The bug here is that dismissing pets after using an invis potion, cancels the potion. But frankly, yes, pets should go invis with the user because they are essentially our weapon/extension of our character. When invis is used for M+ to save time, it is stupid to have hunters in a position where they have to waste time dismissing pets before going invis (or if they forget to do this, they now have a 5min c/d on invis).