[Resolved]Event.current.mousePosition returns different value at same point

code like this:

Code (CSharp):

1. Rect rect;
2.  
3. void OnGUI()
4. {
5.     //...draw some other things...
6.    
7.     if (Event.current.type == EventType.Repaint)
8.     {
9.         rect = GUILayoutUtility.GetLastRect();
10.         if (rect.Contains(Event.current.mousePosition))
11.         {
12.             Debug.Log("mouse over, pos: " + Event.current.mousePosition + " rect: " + rect);
13.         }
14.     }
15.     else if (Event.current.type == EventType.MouseDown)
16.     {
17.         Debug.Log("mouse down, pos: " + Event.current.mousePosition);
18.     }
19. }

Output in Log:
mouse over, pos: (48.0, 27.0) rect: (x:4.00, y:20.00, width:930.00, height:137.00) //Y-aixs value seems incorrect, as there's three lines of text above.
mouse down, pos: (47.0, 64.0)

It's almost the same point in screen, but the Y-aixs value is different. Is there something wrong with my code?

 

Seems it starts at scroll area of EditorGUILayout.BeginScrollView when "mouse over", somehow starts from editor window's left top when "mouse down". Height of Contents above this ScrollView is just 37.0