Came across an issue today where, after a firmware update, a HP LaserJet P4015 decided to send paper from the Letterhead tray through the duplexer. I knew I had seen it before but couldn't recall how it was resolved, but eventually I stumbled across discussions of the same issue. Most refer to the use of an "All_ALM_types_OFF.prn" file which when sent through the printer resolved the issue. It turned out I had a copy of said file lurking in my "I must organise this one of these days" folder. Here's how the PRN file looks in Notepad++, since Notepad and web forums don't render the escape codes correctly: However, this can also be dealt with from the printer's web console. If you want to read about what Alternative Letterhead Mode does when it's on, try this HP page . If you want to know why, years after this issue was first flagged, HP are still shipping firmware which can trip this setting on various models then I have no wisdom for you...