controlling icon order

[Michael Brewer-Davis <michael tech4learning com>]

I have installed a custom mime type with icons, using extension "pxt". 
I'm having trouble getting the custom icons to display in nautilus in 
edubuntu 8.04.  Instead, for these files I see the right file type 
("Pixie image file"), and an executable icon.

When I query gio for the icon types, I get the following icon names:
application-t4l-pixie  // mine
application-x-generic
application-x-executable

Here is the gio code I'm using to get these:
---
  GFile* file = g_file_new_for_commandline_arg(argv[1]);
  GFileInfo* fileInfo = g_file_query_info(...);

  GThemedIcon* icon = (GThemedIcon*) g_file_info_get_icon(fileInfo);

  char** strvals;
  g_object_get((GObject*) themedIcon, "names", strvals, NULL);
---

When I pass this list to gtk_icon_theme_choose_icon(), the chosen icon 
is "application-x-executable".  This agrees with what I see in nautilus.

How can I ensure that my icon is chosen?

Thanks for any help or redirection,
Michael