Why can't I adjust the label size on a Zebra GK420T?

I have a Zebra GK420T connected to a Windows 7 host with 2" x 2" label stock using the stock ZDesigner driver. Whenever I print a document to the printer, only the top 1.2" prints. No matter what settings I adjust, I cannot get the bottom 0.8" to print.

• Printing to the same printer from another computer works
• Printing to the same printer when logged on as another user on the same computer works
• Printing a configuration label shows that it is correctly calibrated and prints along the entire height of the label
• The printer settings all appear correctly configured in both Printer Properties → Advanced → Printing Defaults and in Preferences
• All tests are conducted with Notepad configured for 0 margin in File → Page Setup
• Deleting the printer and re-creating it does not resolve the issue

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