DropAreas work weirdly when they are intersectant

1 DragDropBug1Sample1 and DragDropBug1Sample2 are similiar. But their outputs are different when you do as following.

2 DragDropBug1Sample3 can be tested as following. Notice: the outputs of step 2 and step 4 are empty.
1) Drag red rectangle to green rectangle, and don't release left button. (output---onEntered greenDropArea)
2) Then drag red rectangle to the intersection between green rectangle and blue rectangle, and don't release left button. (output---)
3) Then drag red rectangle to blue rectangle, and don't release left button. (output---onExited greenDropArea onEntered blueDropArea)
4) Then drag red rectangle back to the intersection between green rectangle and blue rectangle, and don't release left button. (output---)
5) Then drag red rectangle to green rectangle, and don't release left button. (output---onExited blueDropArea onEntered greenDropArea)
6) Finally drag red rectangle back to white background. (output---onExited greenDropArea)