Bug 313297 XML data set fail in chart data preview
chart/org.eclipse.birt.chart.ui/src/org/eclipse/birt/chart/ui/swt/CustomPreviewTable.java
glTable.numColumns = 1;
			glTable.marginWidth = 1;
			glTable.marginHeight = 1;
			glTable.horizontalSpacing = 0;
			glTable.verticalSpacing = 0;
			setLayout( glTable );
			cmpHeaders = new Composite( this, SWT.NONE );
			GridData gdCmpHeaders = new GridData( GridData.FILL_HORIZONTAL );
			cmpHeaders.setLayoutData( gdCmpHeaders );
			FormLayout glHeaders = new FormLayout( );
			glHeaders.marginHeight = 0;
			glHeaders.marginWidth = 0;
			cmpHeaders.setLayout( glHeaders );
			cmpHeaders.addMouseListener( this );
		}
		else
		{
			Control[] buttons = cmpHeaders.getChildren( );
			for ( int i = 0; i < buttons.length; i++ )
			{
				buttons[i].dispose( );
			}
		}
		btnHeaders.clear( );
		if ( isDummy )
		{
			for ( int i = 0; i < columnWidths.size( ); i++ )
			{
				addHeaderButton( iHeaderAlignment, "", 
						columnWidths.get( i ) );