Bug 263845 [CommonNavigator] Drag/drop folder from non-Java Proj to Java Proj does copy instead of move sometimes
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
doDropValidation(event);
    }
    /* (non-Javadoc)
     * Method declared on DropTargetAdapter.
     * The mouse has moved over the drop target.  If the
     * target item has changed, notify the action and check
     * that it is still enabled.
     */
    public void dragOver(DropTargetEvent event) {
    	
        Object target = determineTarget(event);
        
        int oldLocation = currentLocation;
        currentLocation = determineLocation(event);
        setFeedback(event, currentLocation);
        
        if (target != currentTarget || currentLocation != oldLocation) {
            currentTarget = target;
            doDropValidation(event);
        }
    }
    /* (non-Javadoc)
     * Method declared on DropTargetAdapter.
     * The user has dropped something on the desktop viewer.
     */
    public void drop(DropTargetEvent event) {
        currentLocation = determineLocation(event);
    	currentEvent = event;
        
        if (!performDrop(event.data)) {