OnCollisionEnter/Exit and Collider edges.

Hello everyone,

I have a project in which when you click on an object you select it. When selected, the object follows the mouse cursor. Now I want to have the selected object jump on top of any other objects that I point my mouse on. Here is my piece of code that controls the mouse movement and object collision detection.

 public bool isSelected;
 
 public List<Collider> currentlyCollidingWith = new List<Collider>();
     public GameObject lastCollidedObject;
 
     void OnCollisionEnter(Collision col){
         currentlyCollidingWith.Add(col.collider);
         lastCollidedObject=col.gameObject;
     }
 
     void OnCollisionExit(Collision col){
         currentlyCollidingWith.Remove(col.collider);
     }
 void OnMouseDown(){
         isSelected=!isSelected;
     }
 
 void FixedUpdate(){
         if(isSelected)
         {
             Vector3 distanceToCam = Camera.main.WorldToScreenPoint(transform.position);
             Vector3 mousePos = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x,Input.mousePosition.y,distanceToCam.z));
             if(currentlyCollidingWith.Count>0)
             {
                 transform.position=new Vector3(mousePos.x,lastCollidedObject.collider.bounds.max.y+gameObject.collider.bounds.extents.y,mousePos.z);
             }
             else
             {
                 transform.position=new Vector3(mousePos.x,gameObject.collider.bounds.extents.y,mousePos.z);
             }
             if(Input.GetKeyUp(KeyCode.Mouse1))
             {
                 transform.RotateAround(new Vector3(transform.position.x,transform.position.y,transform.position.z),new Vector3(0,1,0),45.0f);
 
             }
         }
     }

Also you can see my problem on this video as well:

http://www.youtube.com/watch?v=6ZoeNIA5kTs

The problem occurs only when an object's collider touches the edge of another collider. On such occasions, the collider returns a collision on one frame but no collision on the next frame which causes the object to change positions every frame.

Any help is appreciated. Thank you.