I have just tried actor.enableSmoothMotion() in an almost blank game and I am experiencing something that seems to be a bug.
In this game I have a square that slowly goes from x1 = 600 to x2 = (0 - self width). When it reaches x2 I set its position to x1. I want the square to go from the right to the left side of the screen so that when it disappears from the left side it appears again from the right side. Now the problem is that I can clearly see the square going back from the left side to the right side if I use actor.enableSmoothMotion(). Everything works as expected if I don't use actor.enableSmoothMotion().
I have created a simple test game to show this bug.
EDIT: I used Flash Player to test.