In fixed mode, the global “configure” command is not available
That is, on the “biboumi.localhost” JID, the ad-hoc list does contain only one “configure” not, which is the one for the server JID. It is missing the one for the global JID.
Other global commands like hello, ping or disconnect-from-irc-server are there. So, it’s probably just a conflict in the name of the node, both are called “configure”.