Symbol font does not render in GTK+ 2.0

[Martyn Plummer <plummer iarc fr>]

I find myself unable to render text in the Symbol font to a
GtkDrawingArea. Rendering normal text works fine, but nothing comes out
in the symbol font.  Additionally, the metrics appear to be the same
for every character I try to render (ascent 13, descent 4, width 3).

I'm being as careful as possible with the encoding. The steps I'm
following are
1) Set the font description in the Pango context of the widget to
   Symbol 12
2) Look up the unicode value of the symbol I want to render
3) Convert the unicode value to a utf8 string
4) Create a new layout from the widget's context
5) Set the text of the PangoLayout using the utf8 string
6) Render the layout

I note that gtkfontsel also fails to show anything in the preview pane
when a Symbol font is selected, and if you look carefully (select the
text) you see that a series of very narrow blanks is in fact rendered.

Any suggestions?

Martyn