[2D] Raycast to mouse cursor = offset on Y axis

Hello everyone,

I am trying to learn using raycasts for checking if someone clicks on a 2D sprite object with the mouse and I stumbled upon a really weird little thing: I need to click a certain distance below a clickable sprite in order to click on it.

Say, if you have a rectangle sprite with a 2D box collider, clicking on the rectangle image doesn't yield a hit. Moving the mouse cursor a small distance below the rectangle and clicking in 'empty air' reacts as if you clicked on the collider object. So somehow, the 'hit-detection' between the mouse cursor and the clickable sprite has become shifted on the Y-axis.

I have absolutely no clue how this is possible. And I checked to see if the box collider of the rectangle happens to be offset on the sprite image, but it isn't. Does anyone have a clue on what might be going on? I did try searching for earlier threads on this but couldn't really find anything, or only found problems with no answers.

Could someone explain why this is happening... and how to solve it? My unity is version 4.3.3f1, if that has something to do with it. I'll be trying to find a solution... but this really got me stuck.

The code I use:

 void Update ()
     {
         
         if (Input.GetMouseButtonDown (0)) {
             RaycastHit2D hit = Physics2D.Raycast (Camera.main.ScreenToWorldPoint (Input.mousePosition), Vector2.zero);
 
             if (hit.collider != null) {
                 print ("object clicked: " + hit.collider);
                 print ("object tag: " + hit.collider.tag);
             
             }
 
             if(hit.collider.CompareTag("Exiter")) {
                 print ("Exit the game please!");
                 Application.Quit ();
             }
         
         }
 
     }