Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
private Object element;
		private Item item;
	    UpdateItemSafeRunnable(Item item, Object element) {
	        this.item = item;
	        this.element = element;
	    }
		public void run() {
			doUpdateItem(item, element);
		}