gvfs-mime simply calls "g_app_info_get_default_for_type (mimetype, FALSE);"

that simple command shows the bug as well:

$ python -c 'import gio; print gio.app_info_get_default_for_type("application/x-gnome-saved-search", False).get_name()'
Firefox Web Browser

There is a similar issue described on https://bugs.launchpad.net/ubuntu/+source/gvfs/+bug/949823 with "application/x-java-jnlp-file" files (which is also a subclass of xml)

the issue is in gdesktopappinfo.c get_all_desktop_entries_for_mime_type()

...
  for (i = 0; mime_types[i] != NULL; i++)
...
          /* Pick the explicit default application if we got no result earlier
           * (ie, for more specific mime types)
           */
          if (desktop_entries == NULL)
            {
              entry = g_hash_table_lookup (dir->mimeapps_list_defaults_map, mime_type);
              if (entry != NULL)
                {
                  /* Save the default entry if it's the first one we encounter */
                  if (default_entry == NULL)
                    default_entry = g_strdup (entry);
                }
            }
...

so the code goes through the mimetype and it's subclasses:
application/x-gnome-saved-search -> not in defaults.list, do nothing
text/xml -> ubuntu has firefox.xml listed, it uses it

it doesn't look right to pick the preferred handler for a subclassed mimetype over an available handler for the exact mimetype

would it be better to do something like

"              if (entry != NULL)
...
              else 
               {
                GList *entry_list;
                entry_list = g_hash_table_lookup (dir->mime_info_cache_map, mime_type);
                if (entry_list != NULL)
                  {
                    /* Just pick an handler for the type otherwise */
                    if (default_entry == NULL)
                      default_entry = g_strdup (entry_list->data);
                  }
               }"

i.e "try to get the default handler for the type and if there is none just pick the first handler in the list"?

Created attachment 217520 [details] [review]
Fix default app lookup wrt parent types and defaults.list

There was an issue when looking up the default handler
for a type where a supertype was listed in defaults.list.
We would pick the default for the parent type even if
there was a handler for the more specific type.

In the case of the new-style defaults marking (
"Default Applications" in mimeapps.list) we were already
checking for a more specific handler befor using a default,
but we also need to do a similar check for the defaults.list
case.

the patch indeed fixes the issue!

There is a bug in this where it ignores the defaults.list contents wrongly in some cases, fixed in:

http://git.gnome.org/browse/glib/commit/?id=c35106fcc4a736a2cdd3566042da15216dea415b