Kbase Article of the Week: Mac OS X 10.3, 10.4 and Later: Fonts in Mac OS 9 System Folder Aren‘t Available to Mac OS X Applications →

Apple Support:

Fonts that are in your Mac OS 9 System Folder may not be available to Mac OS X Panther and Tiger applications until you select the System Folder in Classic preferences or start Classic.

– Fonts are unexpectedly substituted in a Mac OS X application.
– Fonts you expect to be available to a Mac OS X application are not.

This can happen when your Mac OS 9 System Folder is on a different volume than Mac OS X, if there are multiple Mac OS 9 System Folders present, or if the font is a bitmap font or font suitcase that contains only bitmap fonts (please note that bitmap fonts are not available in Mac OS X).

I had totally forgotten fonts from a classic system folder could be used by OS X applications, but reading this brought back memories from my run-QuarkXPress-in-Classic-but-everything-else-in-Mac-OS-X-itself days.