Unity new ui Drag and drop

Hi all, i am using unity's new ui to implement drag and drop feature for learning.The problem i am facing is that when i drag a image out of placeholder and drop on empty space it sticks to that as in image.

But if i drag another image and drop it on above any five slots, it successfully placed.Also if i swap two images, one goes to below of that image.Like t$$anonymous$$s,

What i am trying to do is to implement like card games like solitaire.Here is the code. T$$anonymous$$s script goes to image objects like in A, B etc.

public class DragHandler : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler {

 public static GameObject itemBeingDragged;
 Vector3 startPosition;
 Transform startParent;

 #region IBeginDragHandler implementation

 public void OnBeginDrag (PointerEventData eventData)
 {
     itemBeingDragged = gameObject;
     startPosition = transform.position;
     startParent = transform.parent;
     GetComponent<CanvasGroup> ().blocksRaycasts = false;
 }

 #endregion

 #region IDragHandler implementation

 public void OnDrag (PointerEventData eventData)
 {
     transform.position = Input.mousePosition;
 }

 #endregion

 #region IEndDragHandler implementation

 public void OnEndDrag (PointerEventData eventData)
 {
     itemBeingDragged = null;

     if(transform.parent != startParent)
     {
         transform.position = startPosition;
     }

     GetComponent<CanvasGroup> ().blocksRaycasts = true;
 }

 #endregion

}

t$$anonymous$$s script goes to placeholders

public class Slot : MonoBehaviour, IDropHandler {

 public GameObject item
 {
     get
     {
         if(transform.c$$anonymous$$ldCount > 0)
         {
             return transform.GetC$$anonymous$$ld(0).gameObject;
         }
         else
         {
             return null;
         }
     }
 }

 #region IDropHandler implementation
 public void OnDrop (PointerEventData eventData)
 {
     if(!item)
     {
         DragHandler.itemBeingDragged.transform.SetParent(transform);
     }
 }
 #endregion

}