jQuery - changing element position from inside step callback fails
===

I'm trying to create an infinite image slider with jQuery. 

As in, you pass a bunch of images to it, and then clone them to create a repeating sequence.

You click on the next button, the image wrapper moves to the left (using animate()), and when it reaches the first image from the cloned sequence, it seamlessly moves to the first image of the first sequence. So far so good.

I've tried implementing that inside a step callback. Here's the click function, straightforward stuff:

    $next.click(function(e) {
        e.preventDefault();
        $wrapper.clearQueue().animate({
                 left: '-=' + 100
            }, 
            { 
            duration: 300, 
            step: stepCallback
        });
    });

And here's `stepCallback`:

    function stepCallback(pos, fx) {
        if(pos < initialPosition - slidesWidth) {		
            $wrapper.stop(true);
            console.log("stopped");
            $wrapper.css("left", initialPosition);
            // here you'd have, theoretically, some sort of way 
            // to finish the animation at the new position
        }
        // a similar check for the prev button goes here
    }

The animation stops, `stopped` shows up in the console, but `$wrapper.css("left", initialPosition);` has no effect. How come?