Adding the shapes seems to work fine at first, however the list keeping track of shapes in the actor begins overwriting itself. At this point, it is no longer possible to remove the shapes and destroying the actor will leave the shapes in the scene. Things still collide with them as if nothing happened.
Then your game probably crashes because you were expecting those shapes to be removed and whatever their userdata pointed at no longer exists when handling collision events.
Adding the shapes seems to work fine at first, however the list keeping track of shapes in the actor begins overwriting itself. At this point, it is no longer possible to remove the shapes and destroying the actor will leave the shapes in the scene. Things still collide with them as if nothing happened.
Then your game probably crashes because you were expecting those shapes to be removed and whatever their userdata pointed at no longer exists when handling collision events.