FWIW, see https://github.com/mozilla/funfactory/blob/master/funfactory/helpers.py#L48 and note that "New query params will be appended to exising parameters, except duplicate names, which will be replaced." Since `urlparams('', QueryDict('foo=bar&baz=5&foo=ok'))` yields a URL that ends with `"foo=[u'bar',+u'ok']&baz=[u'5']"`, I think `urlparams` is expecting a dictionary where each key has a single value (not a list of values).