PDFRenderer does not presently support out-of-order rendering (e.g., a 10 page document that has an "ending page" fo:page-number-citation in use will have page 10 printed first, then pages 1-9). Turning this value to false has the pages generate in correct order.
xmlgraphics/fop/trunk/src/java/org/apache/fop/render/pdf/PDFRenderer.java