Bug 177504 Engine doesn't provide SubQuery for extended item
Engine doesn't provide SubQuery for extended item, so chart can't use container's binding to execute the query. If possible, engine could provide an option for extended item to choose whether engine could create the query, so extended item won't create SubQuery by itself.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/presentation/LocalizedContentVisitor.java
itemPresentation.setResolution( resolution );
			itemPresentation.setLocale( locale );
			String supportedImageFormats = "PNG;GIF;JPG;BMP;"; 
			IRenderOption renderOption = context.getRenderOption( );
			String formats = renderOption.getSupportedImageFormats( );
			if ( formats != null )
			{
				supportedImageFormats = formats;
			}
			itemPresentation.setSupportedImageFormats( supportedImageFormats ); 
			itemPresentation.setActionHandler( context.getActionHandler( ) );
			
			String outputFormat = getOutputFormat( );
			itemPresentation.setOutputFormat( outputFormat );
			Object rawValue = content.getRawValue( );
			if ( rawValue instanceof byte[] )
			{
				byte[] values = (byte[]) rawValue;
				itemPresentation
						.deserialize( new ByteArrayInputStream( values ) );
			}
			IRowSet[] rowSets = null;
			IBaseResultSet[] rsets = context.getResultSets();
			if (rsets != null)
			{
				rowSets = new IRowSet[rsets.length];
				for (int i = 0; i < rowSets.length; i++)
				{
					rowSets[i] = new RowSet( context, (IQueryResultSet)rsets[i] );
				}