Answer to your edit
You are calling moveToTop()
on a child of the group, so it will only put the image on the op of that specific group. Once you place the second rectangle on the right stage, it gets a higher z-index then the first one your placed and will therefor be 'on top of' the first rectangle (including it's images). To solve this I've set the parent of the image (the group) to move to top on the dragstart, this fixes it for me:
cloneImg.on('dragstart', function(){
this.startX=this.x();
this.startY=this.y();
this.getParent().moveToTop();
});
See also the fiddle: http://jsfiddle.net/Dcevd/3/
PS. If you look in the KineticJS docs, you see that setZIndex is available on Kinetic images (as with all other Shapes). http://kineticjs.com/docs/Kinetic.Image.html