Drag and Drop: Drop does not happens until mouse is moved a bit

when an object is dragged and dropped, sometimes there is a lag with the resulting action. The user needs to do a mouse movement in order to get the action done. In other words, if the user does not move the cursor after dropping an object in a drag&drop action, the resulting action is not triggered until the mouse is moved again.
This can be reprouced with Qt "Draggable Icon" Example.