The attached file causes FAPI+FreeType to error out with a typecheck. Disabling FAPI removes the problem (at the expense of incorrect text). Acrobat Distiller also converts the file to PDF without error, and with the same text as the non-FAPI case.

The problem seems to be caused by a fallback inside the FAPI code. In zfapi.c around line 2308, the code takes a different path with the second glyph, it looks like this should push a BuildChar on the exec stack and execute it, but in fact it doesn't do so. It instead proceeds directly to fapi_finish_render which immediately throws a typecheck error.