Probably happening by selecting duplex in the ribbon instead of the print driver.
It should work that way, but often it doesn't, for reliability sake, always do so in the print driver portion.
We have a new Workcentre 6515. We all use Macs (OS 10.13.3) with Win10 running in a VM using parallels.
Our problem is:
When printing from Windows (eg. Powerpoint) an selecting 2 pages per sheet in the driver settings. Everything gets printed in duplex mode. But duplex is not selected.
Is there any way to solve this?