Thanks for your post. This issue is due to the way mIRC performs a hard disconnect from a server. It applies to both SSL and non-SSL connections.
When you disconnect from the server, or use /disconnect, mIRC sends a QUIT message to the server and then closes the connection immediately. In some situations, this may prevent the server from seeing the QUIT message which can result in the issue you describe.
Many versions ago I changed mIRC to perform a soft disconnect, similar to using the /quit command, where it would send the QUIT message and then wait for confirmation of the closed connection, and any close or quit messages, from the server. If no confirmation was received within a few seconds, mIRC closed the connection automatically. Unfortunately many users complained about the behaviour, so it was removed in a subsequent version of mIRC.
