Don’t change the user’s nick when they join a new room with a different nick
Weirdly, this is exactly the behaviour we explicitely said we didn’t want, in #2695 (closed), be it’s actually how it behaves right now…
So, fix that.
The doc is even wrong about this:
Joining a new channel with a different nick, however, will not change your nick. The provided nick will be ignored, in order to avoid changing your nick on the whole server by mistake. If you want to have a different nickname in the channel you’re going to join, you need to do it explicitly with the NICK command before joining the channel.