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/data/dte/ReportQueryBuilder.java
else if ( image.getImageSource( ) == ImageItemDesign.IMAGE_URI )
			{
				String newImageUri = transformExpression( image.getImageUri( ), query, null );
				image.setImageUri( newImageUri );
			}
			else if ( image.getImageSource( ) == ImageItemDesign.IMAGE_FILE )
			{
				String newImageUri = transformExpression( image.getImageUri( ), query, null );
				image.setImageFile( newImageUri );
			}
			finishVisit( image, query );
			if ( query != value )
			{
				return new IBaseQueryDefinition[]{ query };
			}
			return null;
		}
		/*
		 * (non-Javadoc)
		 * 
		 * @see org.eclipse.birt.report.engine.ir.ReportItemVisitor#visitLabelItem(org.eclipse.birt.report.engine.ir.LabelItemDesign)
		 */
		public Object visitLabelItem( LabelItemDesign label, Object value )
		{
			BaseQueryDefinition query = createQuery( label, value );
			finishVisit( label, query );
			if ( query != value )
			{
				return new IBaseQueryDefinition[]{ query };
			}