If you issue a ""control"" command (/guser, /protect,/ignore,/aop, etc) specifying a nick and mask type e.g. "/protect nick #chan 2 netwk", on a user who is not in the IAL, mIRC sends a 'userhost nick' to obtain the address to add to the list.
However the IAL is not filled for this user from the reply, as it is when you use '/userhost nick'.