1. select a cell
2. try changing its font to "wingdings" (btw, why are all font names lower-case?)

there are two messages on the console:

(gnumeric.exe): GLib-GObject-CRITICAL **: file gobject.c: line 1561 (g_object_re
f): assertion `G_IS_OBJECT (object)' failed

** (gnumeric.exe): CRITICAL **: file pango-engine.c: line 68 (_pango_engine_shap
e_shape): assertion `PANGO_IS_FONT (font)' failed

plus a dialog box saying: 

** ERROR **: file shape.c: line 75 (pango_shape): assertion failed:
(glyphs->num_glyphs > 0) aborting...