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
* 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 (overrideOperation != -1)
    		currentOperation = overrideOperation;
    	
        
        if (!performDrop(event.data)) {
            event.detail = DND.DROP_NONE;
        }