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
assert prop.getTypeCode( ) == PropertyType.ELEMENT_REF_TYPE
				|| prop.getSubTypeCode( ) == PropertyType.ELEMENT_REF_TYPE;
		ElementRefPropertyType refType = null;
		if ( prop.getTypeCode( ) == PropertyType.ELEMENT_REF_TYPE )
			refType = (ElementRefPropertyType) prop.getType( );
		else
			refType = (ElementRefPropertyType) prop.getSubType( );
		refType.resolve( module, prop, ref );
		if ( ref.isResolved( ) )
			ref.getTargetElement( ).addClient( this, prop.getName( ) );
		return ref;
	}
	/**
	 * Checks all value items in the specific property whose type is list
	 * property type. This method is used in command. If any error is found, the
	 * exception will be thrown.
	 * 
	 * @param module
	 *            the module
	 * @param propDefn
	 *            the property definition of the list property
	 * @param list