no support for point 7.10 of xep 0045, registering in a room
The xep about multiuser chat speak of being able to ask to be registered in a room, and there is no menu item to do so in gajim.
I also think gajim do not show a message to admin if such request is sent, but I do know how to test, besides sending this by hand. Ejabberd mod_muc do not support it.
Also see point 9.9, anbd 7.10 (registered nickname) of the xep.