This looks maybe like a bug, don't know if it's really one.
»» http://jsbin.com/ejizib/3/edit
After you move the gray rectangle, there is a tween that changes its position. But the tween starts with the origin position, not the last "drag-end" position.
The tween should start with the drag-end position and go until the x.
parameter. Why doesn't it work on my jsbin?
I got it to work by instantiating the tween inside 'dragend' and removing tween.reset();
rect.on('dragend', function() {
var tween = new Kinetic.Tween({
node: rect,
duration: 2,
x: lenght/2
});
tween.play();
});