Apple Support, explaining a problem no one has had or thought about in a long time:
In a multi-zone network, when you select the last zone, the list of printers in the “Printers” box does not get updated and continues to display the printers that belong to the previous zone that was selected.
The original Apple Printer Utility v1.0 had an issue working with printers in the last zone of a multi-zone network, as well as networks that only have one zone (as that zone is effectively the last zone).
This issue is fixed in later versions of the Apple Printer Utility. To find the most recent version of this software, refer to the Apple Software Updates Library at http://www.apple.com/swupdates.