I encountered a server today which responded to /LIST thusly...

-> irc.server.com LIST
<- :irc.server.com 481 yournick :Permission Denied: Insufficient privileges

mIRC did not realize that 481 was the server's official response to the /LIST command, and continued to await 321/322/323 channel listings data from the server forever (as evidenced by my re-typing /LIST producing only "* /list: listing in progress...").

I presume that's not a mIRC bug, because I believe 481 isn't a LIST-specific server response (i.e., mIRC has no way of knowing that 481, in such a case, is the server's response to /LIST).

However: I also noticed that upon later disconnecting from that server with /QUIT, mIRC's channel listing window suddenly appeared "out of nowhere", showing 0 channels.

After a little more experimentation (including verifying this also happens with the /DISCONNECT command), I felt that this behavior might count as a bug. Specifically: once mIRC's internal 321/322/323 event "listener" is started by /LIST, it appears that mIRC forgets to cancel/abort it if /QUIT or /DISCONNECT happen before 321 arrives.

(Which means this bug would also affect people who run /LIST on a server that has become non-responsive and who then /QUIT or /DISCONNECT -- not just people using a server that responds 481 to /LIST. smile )