问小程序后台最低基础库设置部分失效？

你好，我们在小程序后台设置了基础库最低版本库1.7.4  ，然而却有客户端基础库 1.1.1的用户进来了。

用户系统信息：

"system":"iOS 11.4.1","errMsg":"getSystemInfo:ok","model":"iPhone 7 Plus<iPhone9,2>","pixelRatio":3,"windowHeight":672,"screenWidth":414,"screenHeight":736,"windowWidth":414,"language":"zh_CN","version":"6.5.7","platform":"ios","SDKVersion":"1.1.1"