MongoDB"userAdminAnyDatabase"用户无法在"任何数据库"中管理用户.为什么？

这是一个userAdmin与userAdminAnyDatabase问题.

在system.users我有以下用户(1234两者的密码):

> db.system.users.find()
{ "_id" : ObjectId("52a976cb7851682aa44d6d4d"), "user" : "admin_one", "pwd" : "884f516cf308a4c6a75bbc5a0a00807b", "roles" : [  "userAdmin",  "dbAdmin" ] }
{ "_id" : ObjectId("52a97c697851682aa44d6d4f"), "user" : "admin_two", "pwd" : "26e7bb644e5919461cd6ba7403dc6906", "roles" : [  "userAdminAnyDatabase",  "dbAdminAnyDatabase" ] }

与错误的用户连接:

$ mongo mono -u admin -p 1234
connecting to: mono
Thu Dec 12 10:09:00.733 Error: 18 { code: 18, ok: 0.0, errmsg: "auth fails" } at src/mongo/shell/db.js:228

这没关系.

与数据库管理员连接:

$ mongo mono -u admin_one -p 1234
connecting to: mono
> db.system.users.find()
{ "_id" : ObjectId("52a976cb7851682aa44d6d4d"), "user" : "admin_one", "pwd" : "884f516cf308a4c6a75bbc5a0a00807b", "roles" : [  "userAdmin",  "dbAdmin" ] }
{ "_id" : ObjectId("52a97c697851682aa44d6d4f"), "user" : "admin_two", "pwd" : "26e7bb644e5919461cd6ba7403dc6906", "roles" : [  "userAdminAnyDatabase",  "dbAdminAnyDatabase" ] }

哪个也行.

现在,连接"AnyDatabase"管理员我收到一个错误:

$ mongo mono -u admin_two -p 1234
connecting to: mono
> db.system.users.find()
error: { "$err" : "not authorized for query on mono.system.users", "code" : 16550 }

为什么？