For apps that render as PCXML, if you try to download it to PDF, the chart does not appear. It shows up on the browser, but not in the PDF.
I've attached a YXMD that illustrates the issue. I also attached the PCXML that it produces. When you open the PCXML, you will see all the charts. When you save the PCXML to PDF, you get the attached PDF, which illustrates the issue (no charts, just the grouping titles).