Thats not how a bnc works when hes not really joining new channels so this request sounds useful.
[21:30:30] (SHiZNO): so here's how attaching works...
[21:30:35] (SHiZNO): your client connects to znc
[21:30:53] (SHiZNO): znc loops through all of the channels that it is currently joined to
[21:31:19] (SHiZNO): for each channel that is not detached (znc setting) ... it will send a JOIN to the incoming client
[21:31:35] (SHiZNO): so your client never actually sends a join in this scenario
[21:32:27] (SHiZNO): the way irc works in general is that you type "/join #foo" in your client and then the client processes it and sends "JOIN :#foo" to the ircd
[21:33:09] (SHiZNO): then the server processes that and decides to join you to the channel or not (ex. makes sure +i or +k are enforced, etc.)
[21:34:41] (SHiZNO): if you can join, then it sends your client back a "JOIN :user!ident@host.com #channel" <-- that may be backwards
[21:34:49] (SHiZNO): and that tells your client to open the window
[21:35:01] (SHiZNO): so what znc does, is fakes that last command for each channel that it is already in
[21:35:22] (SHiZNO): which lets your client know that it just joined (even though it never sent a JOIN)
[21:36:34] (SHiZNO): your best hope would probably be if mIRC has an option for not popping up a channel at all by default, without needing the -n
p.s im not trying to teach you how irc work by pasting this.
tbh i learned when he told me
its just to let you (and others) know how znc works