It just came to my attention that class-based kerning isn't being applied to ligatures in a number of my fonts. Here's the class definition:
%%GLYPHS i' fi ffi dotlessi iacute icircumflex idieresis igrave imacron iogonek itilde dottediacute
%%KERNING R 0
The fi and ffi glyphs are so named in the fonts, and swap out just fine. Any ideas?