其实这是keychain的一个bug，可以去github搜一下.

Actually, this is a bug of keychain, you can search it at github.

Github 34018 问题

几个月前，苹果的一些员工来我们公司给我们讲课，课后我们问了这个问题，他们也没有给我们解决方案

A few months ago, some apple's staff came our company to give us a course, after course,we asked this question, they also did't give us a solution