The mauler is a wild animal. There is nothing but instinct that controls him, even before the Ego Whip.
The vanes of the windmill only had air to drag them. Which is not much, and clearly allows a lot of force to build. With the count and three more knights after
some time, the result would be different.
When you was running down a hill you performed an action which was keeping balance.
The mauler has the the ground to drag its legs and can't perform any action. There is no such action as stopping. The action is charging. Charge is a full-round action, that starts and finnish in a single round. The animal is doing a full-round action when it shouldn't be doing anything except letting the momentum drag him forward on the ground, without moving its legs.
Just like in this:
http://www.youtube.com/watch?v=DOPJsj9efIc
The rhino is killed, it gives 5 steps and falls, the ground producing enough drag to slowly it down harmlessly.