I reverted back to v3 drivers, which solved the problem.
I'm confused by the behaviour of the option "Change Document Size" in Xerox Print Experience 5.1. Even though all tray settings on the printer says A4, the app keeps reverting to Letter size for this option, and needs to be manually changed each time a person creates a print job.
I have checked that the printed document does not overwrite paper sizes.
Solved! Go to Solution.