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
currentOperation = DND.DROP_NONE;
        currentEvent = null;
    }
    /* (non-Javadoc)
     * Method declared on DropTargetAdapter.
     * Last chance for the action to disable itself
     */
    public void dropAccept(DropTargetEvent event) {
    	currentEvent = event;
    	if (!validateDrop(currentTarget, event.detail, event.currentDataType)) {
            currentOperation = event.detail = DND.DROP_NONE;
        }
    	currentEvent = null;
    }
    /**
     * Returns the bounds of the given SWT tree or table item.
     *
     * @param item the SWT Item
     * @return the bounds, or <code>null</code> if it is not a known type of item
     */
    protected Rectangle getBounds(Item item) {
        if (item instanceof TreeItem) {
            return ((TreeItem) item).getBounds();
        }
        if (item instanceof TableItem) {
            return ((TableItem) item).getBounds(0);
        }
        return null;