Wow. I figured out the issue! When you add a printer on the Mac, it autoselects the print driver. By default, it uses the AirPrint driver: This driver has the bug that will only print fit-to-paper. If you manually select "Samsung C3060 Series", the printer prints sizes correctly. Please do escalate the AirPrint bug though. This was incredibly difficult to troubleshoot, and the AirPrint driver shouldn't have this issue either.
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