Sometimes the wrong DragHandler reacts

In a Window I have multiple draggable items of the same type. 

When I try to drag one of these items then sometimes an arbitrary other item reacts and not the one under the mouse.

To show this effect I attach a minimal example together with a logfile and screenshot I created with it.

If you start the example then you see four blue rectangles in a Window.

These rectangles use a DragHandler in order to react on drag events. When you start dragging one of them then the color changes to red. When you drag to another ractangle then it accepts the drag event and changes its color to green.

But sometimes you will see that not the rectangle under the mouse changes to red but another one. See the attached screenshot:

 The mouse pointer on the screenshot is not at the exact pixel of the drag start but it is still within rectangle 2 where I started the action. But rectangle 3 is red which is the wrong one.

Now have a look into the output log:

The last message telling "rectangle 3 DragHandler: active = true" reports a centroid position of (250, -129). This position is not within rectangle 3 but it it within rectangle 2.

Up to now I did not see this effect on Linux but only on Windows.