This is done to fix the following bug: in MySQL if you set max_user_connections run-time, then existing connections won't be counted. You can set it to 10, but a user can already have a thousand of connections and he'll be able to open ten more.

A possible fix would be always to count user connections, but it would introduce an overhead for those many users, who don't use connection limits. MariaDB has implemented a different fix — don't count connections if started with max_user_connections=0, but don't allow max_user_connections to be set to non-zero value, because a correct connection counting in that case cannot be guaranteed.

There are other ways to fix this bug, we can consider them.

I would like to see MariaDB use some other solution, so that max_user_connections is truly a dynamic variable.

kolbe, yes, exactly. That's why it's a "Task", not a "Bug", and that's why it's not closed as "Won't Fix".