Reproducible bug in mIRC 7.52:
1. Connect successfully to a server of your choice that uses SSL, ex. EFnet: irc.choopa.net port +9999 (for SSL)
2. Disconnect from the server (via File -> Disconnect or timeout)
3. Choose File -> Select Server...
4. Pick a server from the Connect -> Servers menu that has a non-SSL configuration than in step #1, ex. EFnet: irc.mzima.net port 6667 (non-SSL)
5. Click Select
6. Click Connect -- client will attempt to connect to the latter server name, but with the previous servers' port/config (ex. irc.mzima.net port +9999)
Note that checking the "New Window" checkbox *does not* work around this problem -- the new window/tab will still use the incorrect port/config.
Workaround:
After disconnecting from a server, fully close the entire window/tab for that particular server before making a new one.
Hopefully this description is understood/suitable! I can provide relevant .ini files if needed.