Bug 125272 [Viewers] AbstractTreeViewer needs remove(Object parentElement, Object[] childElements)
There is an add(Object parentElement, Object[] childElements) but no corresponding remove(). Without this method, if you have an element that appears under multiple parents, the only way to get model and viewer in sync after removing the element from just one of its parents is calling refresh().
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
}
        }
        return result.toArray();
    }
    /**
     * Returns whether the node corresponding to the given element or tree path is expanded
     * or collapsed.
     * 
     * @param elementOrTreePath
     *           the element
     * @return <code>true</code> if the node is expanded, and <code>false</code>
     *         if collapsed
     */
    public boolean getExpandedState(Object elementOrTreePath) {
        Assert.isNotNull(elementOrTreePath);
        Widget item = internalGetWidgetToSelect(elementOrTreePath);
        if (item instanceof Item)
            return getExpanded((Item) item);
        return false;
    }
    /**
     * Returns the number of child items of the given SWT control.
     * 
     * @param control
     *           the control
     * @return the number of children
     */
    protected abstract int getItemCount(Control control);
    /**
     * Returns the number of child items of the given SWT item.