This bug applies to all motion tricks:
-mass exodus
-add motion
-mass add motion

When a player is riding another entity, and is controlling that entity's motion (Ex: riding a pig AND holding carrot on a stick, or Riding a horse WITH a saddle), any motion tricks applied to that entity will reset its velocity to 0 rather than accelerating it.

This was a duplicate of #490, apparently.

Not that I'm blaming you, they seemed different enough before I started working with the other issue.

Closed with 3ca0a13