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
private int lastValidOperation;
    
    /**
     * The current DropTargetEvent, used only during validateDrop()
     */
    private DropTargetEvent currentEvent;
    
    /**
     * The data item currently under the mouse.
     */
    private Object currentTarget;
    /**
     * Information about the position of the mouse relative to the
     * target (before, on, or after the target.  Location is one of
     * the <code>LOCATION_* </code> constants defined in this type.
     */
    private int currentLocation;
    /**
     * A flag that allows adapter users to turn the insertion
     * feedback on or off. Default is <code>true</code>.
     */
    private boolean feedbackEnabled = true;
    /**
     * A flag that allows adapter users to turn auto scrolling
     * on or off. Default is <code>true</code>.
     */
    private boolean scrollEnabled = true;
    /**
     * A flag that allows adapter users to turn auto
     * expanding on or off. Default is <code>true</code>.