currently schema_list will iterate over the default SchemaSource
list, and not the one associated with the passed in Schema. This
means schema_list can give incorrect results for a Schema fetched
from a non-default SchemaSource, like via new_from_directory.

I was just trying some code via pygobject and hit this. I was basically doing:

   schema_source = Gio.SettingsSchemaSource.new_from_directory(
           "/my/test/dir", None, True)
   schema = schema_source.lookup(app_id, True)
   settings = Gio.Settings.new_full(schema, None, None)
   print settings.list_children()

Which didn't list expected results, the list was empty. However if I added this before the code:

   os.environ["GSETTINGS_SCHEMA_DIR"] = "/my/test/dir"

list_children() would return the expected results