Sometimes when you select A3, the printer prints out on A4 paper. To fix this and make sure A3 print jobs, print out on A3 paper instead of A4, check the following:
- Check that the tray contains A3
- Check that the printer (from the web interface) has the tray set to A3
- Check that the printer driver has the correct tray set to print A3 instead of A4
In some cases, you may need to set the print driver (logical printer) settings to A4, apply the setting, then set it back to A3 (Under the Advanced tab -> Printing Defaults and General tab -> Printer Preferences).