Bug 232777 [Viewers] ViewerDropAdapter holds currentTarget forever
Build ID: 3.3.2 Member currentTarget should be set to null after drop or after cancel, because it holds a domain object, which can't be garbage collected after Viewer.setInput(null).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
/**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * slightly before the target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_BEFORE = 1;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * slightly after the target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_AFTER = 2;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * directly on the target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_ON = 3;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is not positioned
     * over or near any valid target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_NONE = 4;