Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* <p>
	 * References can be in two states: resovled and unresolved. An unresolved
	 * reference is just a name, but the system has not yet identified the
	 * target structure, or if a target even exists. A resolved reference caches
	 * a pointer to the target structure itself.
	 * 
	 * @param oldRef
	 *            the old reference, if any
	 * @param newRef
	 *            the new reference, if any
	 * @param prop
	 *            definition of the property
	 */
	protected void updateReference( StructRefValue oldRef,
			StructRefValue newRef, ElementPropertyDefn prop )
	{
		ReferencableStructure target;
		
		
		if ( oldRef != null )
		{
			target = oldRef.getTargetStructure( );
			if ( target != null )
				target.dropClient( this );
		}
		
		
		
		if ( newRef != null )
		{