Bug 191005 PDF preview hangs up with attached xtab.[1102]
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/layout/pdf/PDFStackingLM.java
{
		super( context, parent, content,  executor );
	}
	protected boolean layoutChildren( )
	{
		initialize( );
		boolean hasNextPage = false;
		hasNextPage = traverseChildren( );
		if ( !hasNextPage )
		{
			isLast = true;
			clearCache();
		}
		else if(!context.isAutoPageBreak( ))
		{
			clearCache();
		}
		if ( !isRootEmpty( ) )
		{
			closeLayout( );
			hasNextPage = !submitRoot( ) || hasNextPage;
		}
		return hasNextPage;
	}
	protected  boolean clearCache()
	{
		return true;
	}
	
	protected boolean isRootEmpty( )