HP Color Laserjet Pro duplex printing is flipped.

[qbee42]

Color-LaserJet-Pro-MFP-3301

Regardless of duplex long-side or short-side, portrait or landscape, the back side of a portrait duplex document is always upside down. The solution is to copy and edit the default PPD file to comment out the * cupsBackSide: Rotated line like this:

*DefaultDuplex: None
*Duplex None/Off: "<</Duplex false>>setpagedevice"
*Duplex DuplexNoTumble/On (Portrait): "<</Duplex true/Tumble false>>setpagedevice"
*Duplex DuplexTumble/On (Landscape): "<</Duplex true/Tumble true>>setpagedevice"
*CloseUI: *Duplex
*% cupsBackSide: Rotated

Save that file and modify the printer in CUPS to use the new PPD file.