memcache не работает должным образом

У нас есть небольшое приложение для Google App Engine на Python, и мы используем memcache. Но ключи memcache остаются даже после memcache.delete, а также memcache возвращает число (0), когда я ожидаю, что он вернет строку ("undefined"). Вот мой код:

check_feature.py:

import sys
sys.path.insert(0, 'libs')

import webapp2
import json
from google.appengine.api import memcache
from models.shard_counter import GeneralCounterShard
from models.check_feature_limit import CheckFeatureLimit


class CheckFeatureHandler(webapp2.RequestHandler):
    def get_number_of_users_enabled(self, feature_name):
        """
        Get the number of users enabled for the given feature name.
        """
        number_of_users_enabled_undefined = "undefined"
        number_of_users_enabled = memcache.get(key=feature_name)
        if (number_of_users_enabled is None):
            check_feature_limit = None
            check_feature_limits = CheckFeatureLimit.gql("WHERE feature_name=:1 ORDER BY last_modified DESC LIMIT 1", feature_name)
            if (check_feature_limits.count() > 0):
                check_feature_limit = check_feature_limits.get()
            if (check_feature_limit):
                number_of_users_enabled = check_feature_limit.number_of_users_enabled
            if (number_of_users_enabled is None):
                number_of_users_enabled = number_of_users_enabled_undefined
            memcache.add(key=feature_name, value=number_of_users_enabled, time=3600)
        if (number_of_users_enabled == number_of_users_enabled_undefined):
            number_of_users_enabled = None
        return number_of_users_enabled

admin.py:

import sys
sys.path.insert(0, 'libs')

import webapp2
import json
import requests
from google.appengine.ext.webapp import template
from google.appengine.api import memcache
from models.shard_counter import GeneralCounterShard
from models.check_feature_limit import CheckFeatureLimit

template.register_template_library("tags.tags")


class AdminHandler(webapp2.RequestHandler):
    def get(self):
        self.post()

    def post(self):
        params = {}
        number_of_users_enabled_dict = {}
        number_of_users_dict = {}
        r = requests.get(url="http://jsons.[part_of_link_suppressed].com.s3.amazonaws.com/flags.json")
        flags = json.loads(r.text)
        if ((flags) and ("depending_on_counter" in flags) and (len(flags["depending_on_counter"]) > 0)):
            for feature_name in flags["depending_on_counter"]:
                check_feature_limit = None
                check_feature_limits = CheckFeatureLimit.gql("WHERE feature_name=:1 ORDER BY last_modified DESC LIMIT 1", feature_name)
                if (check_feature_limits.count() > 0):
                    check_feature_limit = check_feature_limits.get()
                number_of_users_enabled = self.request.get(feature_name + "_number_of_users_enabled")
                if (number_of_users_enabled):
                    number_of_users_enabled = int(number_of_users_enabled)
                    if (not(check_feature_limit)):
                        check_feature_limit = CheckFeatureLimit(feature_name=feature_name)
                    check_feature_limit.number_of_users_enabled = number_of_users_enabled
                    check_feature_limit.put()
                    memcache.delete(key=feature_name) # I don't think it works.
                number_of_users_enabled = None
                if (check_feature_limit):
                    number_of_users_enabled = check_feature_limit.number_of_users_enabled
                if (not(number_of_users_enabled is None)):
                    number_of_users_enabled_dict[feature_name] = number_of_users_enabled
                number_of_users = GeneralCounterShard.get_count(feature_name)
                number_of_users_dict[feature_name] = number_of_users
            params["depending_on_counter"] = flags["depending_on_counter"]
            params["number_of_users_enabled_dict"] = number_of_users_enabled_dict
            params["number_of_users_dict"] = number_of_users_dict
        html = template.render("admin/admin.html", params)
        self.response.out.write(html)

app = webapp2.WSGIApplication([
    ("/admin", AdminHandler)
], debug=True)

Значения test_counter_feature_1 (Число пользователей для включения) равно 2, test_counter_feature_2 равно 4, а test_counter_feature_3 не определено (объекта нет), но в memcache значения равны 2, 3 и 0 соответственно, даже после сохранения формы (и поэтому memcache следует удалить). В чем проблема? Я ожидаю, что значение test_counter_feature_3 будет "неопределенным", а не 0. И еще два значения должны быть удалены после сохранения формы.