Mac printer presets ignored, LR always prints duplex

Printer is a HP Color Laserjet Pro M478. Computers are two MacBook Pros and a Mac Mini running the most current software. The issue is the same on all three computers. 

When printing from LR, no matter what choices I make, eg choosing a single-side preset, or unclicking "print on both sides" my prints are printed duplex (on both sides of the paper. I even created a new preset from within the "print settings" dialog in LR for single-sided prints. No dice, it still duplexed the pages. 

How can I get one-sided prints other than by printing one page at a tme?

On checking, I am having the same problem in Reader, thought fewer choices are available there. All of my non-Adobe products (eg Microsoft Office, Mail, Safari, Chrome, Apple Photos, Calendar, etc) are working correctly, eg duplex when duplex is chosen, single-sided when it is not, so it doesn't appear to be any sort of issue with the printer or system side drivers.

This is a new printer, my prior printer did not have a duplexer.