With new models of HP printers we've noticed problems with AS400's printing directly to tray 1. If the printer will be used as an AS400 printer, make the following changes to allow for platform print being sent to tray 1.
From the printer's web interface, select the settings tab
Browse to the following Menu: Configure Device -> System Setup -> Tray Behavior
Set Use Requested Tray to First (default is Exclusively). This will allow print coming to tray one to be redirected to the next available tray without user interaction.