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
return;
		if ( extendsRef.isResolved( ) )
			return;
		
		
		
		
		
		
		ElementDefn metaData = (ElementDefn) getDefn( );
		PropertyDefn propDefn = (PropertyDefn) metaData
				.getProperty( IDesignElementModel.EXTENDS_PROP );
		int ns = metaData.getNameSpaceID( );
		DesignElement resolvedParent = module
				.resolveElement( ReferenceValueUtil.needTheNamespacePrefix(
						extendsRef, module ), ns, propDefn );
		if ( resolvedParent != null && isExtendsValid( resolvedParent ) )
		{
			extendsRef.resolve( resolvedParent );
			resolvedParent.addDerived( this );
		}
	}
	/**
	 * Gets the name of the element that this element extends.
	 * 
	 * @return The name of the extended element.
	 */
	public String getExtendsName( )
	{
		if ( extendsRef == null )