Printing: HP M479fdw prints extra page reading "PDF"

Using an M479fdw with Debian desktop and laptop machines. It's worked fine for a while, but recently began spitting out an extra blank page at the end of each job. The blank page says "PDF" at the top, but no other text or image is printed.

CUPS printers.conf entry: "HP Color LaserJet Pro M478f-9f, driverless, cups-filters 1.28.5".

Thanks for any advice.