ff was (usually) setting the ascent/descent fields of the 'hhea' table to
0. When the font was drawn on the mac it was clipped to nothing.
Caveat: Old sfd files are still broken and
there is no UI for fixing them. Instead you must edit them manually, and
change:
HheadAOffset: 0
HheadDOffset: 0
to be:
HheadAOffset: 1
HheadDOffset: 1