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
e = e.getExtendsElement( );
		}
		return null;
	}
	/**
	 * Gets the cached parent element. There will be no parent if either 1) the
	 * element does not extend from another user-defined element, or 2) the
	 * extends element is undefined.
	 * <p>
	 * Part of: Inheritance system.
	 * 
	 * @return parent element
	 */
	public DesignElement getExtendsElement( )
	{
		if ( extendsRef == null )
			return null;
		if ( !extendsRef.isResolved( ) )
			resolveExtends( getRoot( ) );
		return extendsRef.getElement( );
	}
	/**
	 * Resolves the parent element reference.
	 * 
	 * @param module
	 *            the module information needed for the check
	 */
	public void resolveExtends( Module module )
	{
		if ( extendsRef == null || module == null )